Leading figures in Chad, including ex-ministers, former presidential advisers and MPs, have called for the military council to concede to a more inclusive transition following the death President Idriss Déby in April.
He died of his injuries following clashes with rebels in the north of the country - and a day after provisional election results projected he would win a sixth term in office.
The government and parliament were dissolved and his son, 37-year-old four star general Mahamat Idriss Déby Itno, took over, saying the military council would be in control until elections were held within 18 months.
But the appeal, signed by about 20 people, including Bédoumra Kordjé, a former minister and current vice-president of the African Development Bank, wants the charter of the military council to be changed so more groups can have a say in the transition.
They also want a national conference to be set up within three months to debate Chad’s political future with an international facilitator in charge.
Déby had spent more than three decades in power and was one of Africa's longest-serving leaders.
He was accused of stifling dissent ahead of April’s election - and most prominent opposition leaders withdrew from the race.
An army officer by training, he was a long-time ally of France and other Western powers in the battle against jihadist groups in the Sahel region of Africa.
There are reports of fresh clashes on the border between the Central African Republic (CAR) and Chad.
The clashes come just days after six Chadians and three Russians were killed in fighting at a border post.
For the past few years, Russia has sent soldiers to assist the CAR's military but it is rare for Moscow to confirm its involvement in the fighting.
The UN mission to the CAR says the situation remains tense, while Chad is sending more forces to the border.
Both countries have called on the UN and the African Union to investigate last week's incident.
Amnesty International has asked Chad to ensure that officers responsible for killing protesters during demonstrations in April and May are prosecuted.
The demonstrators were calling for the return of constitutional order after President Idriss Déby Itno died of his injuries on 20 April following clashes with rebels in the north of the country.
His son, 37-year-old four star general Mahamat Idriss Déby Itno, took over, leading a military council until elections are held.
The protests which followed were banned and met with brutal force by the security forces.
Hundreds of demonstrators were arrested and dozens died.
Amnesty International and other rights organisations have in the past called for an investigation into the deaths.
Africa editor, BBC World ServiceCopyright: AFP
The government of Chad has accused the Central African Republic (CAR) of killing six of its soldiers and wounding five others in an attack in the south of the country.
Chad's Foreign Minister, Cherif Mahamat Zene, said troops from the CAR killed a soldier on Sunday morning in Sourou.
He said they kidnapped five others who were then killed close to the border.
A senior Chadian security official told the French news agency that the soldiers were pursuing rebels.
The government in the CAR capital, Bangui, often accuses Chad of trying to destabilise the country by supporting rebels.
US prosecutors have opened a case against Chadian diplomat Mahamoud Adam Bechir, his former deputy and his wife for allegedly taking a bribe from a Canadian oil company.
The three had promised the company oil deals from their country and were given $2m ($1.4m), according to the US Justice Department.
Mr Bechir was at the time the ambassador to the US.
He is now Chad's ambassador to Russia and presented his credentials to the Russian president on 18 May, according to photos from the Russian News Agency Tass.
The three have not commented.
The founding shareholder of the Canadian firm, Naeem Tyab, was arrested in 2019 and pleaded guilty to bribery charges, the justice department said.
The three Chadians are yet to be arrested.
Africa editor, BBC World Service
The African Union (AU) has called for a democratic transition in Chad within 18 months following last month's military takeover.
The AU said it categorically rejected any extension of the transition period.
Chad's military council has promised to hold elections within 18 months.
It is headed by the son of the former president, Idriss Déby, who died last month after being injured fighting rebels.
There have been regular opposition protests since the military took over, with dozens of activists arrested.
You may want to watch:
BBC correspondent Mayeni Jones looks at conflicting desires for democracy and security in Chad following the death of President Idriss Déby.
BBC News, Abuja
Chad’s new military leader has been in Nigeria for talks with President Muhammadu Buhari to shore up regional support for his regime.
Lt Gen Mahamat Idriss Déby Itno, 37, heads a military council after his father, President Idriss Déby, died of injuries sustained during clashes with rebels last month.
Chad is a key ally in the fight against Islamist groups in the Sahel region of Africa - in particular the Nigeria-based militants Boko Haram.
"Nigerians know and appreciate the role Chad played in helping us to combat terrorism, and we will continue the collaboration,’’ Mr Buhari said in a statement after their meeting in Nigeria's capital, Abuja.
The Nigeria president, himself a former military ruler, offered his support to Lt Gen Déby in helping him return Chad to democratic rule, which the military council has said will happen within 18 months.
The new leader of Chad is in neighbouring Niger where he's had a one-on-one meeting with the president, weeks after being appointed.
Gen Mahamat Déby Itno was installed as leader of Chad's transitional military council after his father - President Idriss Déby - died from battlefield injuries while fighting rebels close to the Libyan border.
On Monday Gen Déby Itno thanked President Mohamed Bazoum for a warm welcome, calling him his "brother".
"We came here to reaffirm our friendship and to thank President Bazoum for his support since the death of the Marshal - may God have mercy on his soul.
Both Chad and Niger are among the Western-backed "G5" countries fighting Islamist militants in the Sahel region.
"We have a force here in Niger in Tera - a contingent of the G5 Sahel - we came to support them, knowing that they lost the Marshal of Chad, supreme chief of the army - we came to offer our condolences and to give them moral support," said Gen Déby Itno.
More about Chad's new leader:
Africa editor, BBC World Service
The military in Chad has claimed victory against northern rebels following weeks of fighting.
The conflict against Libya-based rebels threw the country into a crisis when President Idriss Déby died after being wounded on the frontline last month.
The military takeover under the leadership of Mr Déby’s son has been condemned by the opposition and civil society groups leading to protests.
Sunday's victory parade was aimed at boosting the popularity of the Chadian military at a time of great uncertainty in the country.
Some people in the capital N'Djamena cheered as soldiers returned from the frontline in a column of tanks and armoured vehicles.
Journalists were shown dozens of captured rebels at an army base.
But it's worth remembering that weeks ago we were told the rebel group Front for Change and Concord in Chad (Fact) had been defeated - only for fighting to resume.
It's not clear if the Libya-based rebels still have the capacity to be a threat to the military council now running the country.
In recent weeks protests demanding a return to civilian rule have been violently broken up by the security forces.
Africa editor, BBC World Service
Activists in Chad say at least 10 people have been injured and 15 arrested during protests in the capital, N'Djamena, on Saturday.
Police fired tear gas and one person was wounded by a live bullet.
A coalition of opposition parties called for the demonstrations against the recent military takeover following last month's battlefield death of President Idriss Déby.
Protestors denounced what they called a monarchy following the naming of Mr Déby's son as president.
The transitional military council says it will hold elections within eighteen months, but the opposition wants a civilian in charge.
BBC World Service
Military leaders in Chad - who took over after the death of the country's long-standing ruler Idriss Déby last month - have named a transitional government.
An army spokesman said 40 ministers and their deputies had been appointed. They include a former rebel chief - Acheick Ibn Oumar - who will head a new national reconciliation ministry.
One senior opposition figure Saleh Kebzabo said he recognised the authority of Chad's transitional government, and several other long-time opponents of the former president were given portfolios.
But other opposition figures say the military council - led by Mr Déby's son Mahamat Idriss Déby Kaka - has carried out an institutional coup, and say they won't be satisfied until it appoints a civilian president.
The announcement came hours after the ruling military council had lifted an overnight curfew that was imposed following the president's death last month, during fighting against rebels.
There has been international concern for the stability of Chad in recent weeks, as a rebel group has tried to advance on the capital N'djamena.
The military says it has stemmed their advance, and killed hundreds of the rebels from the group Front for Change and Concord in Chad (Fact).
The United Nations Human Rights Commission says it is deeply disturbed by events in Chad, where security forces opened fire this week on people protesting against the recent military takeover.
At least six people were killed on Tuesday in the capital, N’Djamena, and in Moundou. More than 650 people were arrested.
The UN commission condemned the disproportionate use of force and called on the authorities in Chad to respect human rights, including the right to peaceful assembly.
It criticised a decree imposing a blanket ban on demonstrations that are not given prior authorisation and called for a return to civilian rule and constitutional order.
The violence follows the death last week of President Idriss Déby. The 60-year-old, who had ruled Chad for 30 year, died after being wounded on the front line in clashes with advancing rebels.
Fighting has been taking place in the west of Chad between the military and rebels who launched an insurgency earlier this month from bases in Libya.
A spokesman for the country's military council said the fighting was in the Kanem region near the border with Niger.
It is close to where former President Idriss Déby was fatally wounded whilst visiting troops on the front line 10 days ago.
On Sunday the military council, led by the former president's son, said there would be no negotiating with the rebel group, known as Fact.
Earlier this week at least six people were killed in clashes between security forces and demonstrators protesting against the military takeover.
At least five people have been killed during Tuesday's protests against the military takeover in Chad, prosecutors said.
"There were four deaths in N'Djamena," including "one killed by the demonstrators", AFP news wire quotes the the capital's prosecutor Youssouf Tom as saying.
A fourth person was killed in the southern city of Moundou, another prosecutor told AFP.
At least 12 Chadian soldiers have been killed near Lake Chad following an attack on their base by Islamist militants, local authorities say.
Forty jihadists where also killed after the attack on Monday morning in the Kaya district, according to local governor Mahamat Fadoul Mackaye.
The area is also home to a base for Islamists groups including Boko Haram and the Islamic State West Africa Province (Iswap), AFP reports.