Veteran warlord Gulbuddin Hekmatyar has returned to the Afghan capital, eight months after signing a peace deal with the government.
Mr Hekmatyar, an Islamist warlord accused of numerous atrocities, leads Hezb-e-Islami, the country's second largest militant group.
Under the deal, he has agreed to accept the constitution and abandon violence.
Some see the deal as a step forward for Afghanistan but others say it could exacerbate divisions in the government.
Gulbuddin Hekmatyar travelled to the capital from Jalalabad amid tight security, his convoy guarded by an Afghan army helicopter.
President Ashraf Ghani led an event to welcome him at the presidential palace and thanked him for "heeding the peace call".
Mr Hekmatyar urged the Taliban to hold peace talks, saying: "Let's end the war, live together as brothers and then ask foreigners to leave our country."
On Friday, he will lead prayers at a prestigious mosque.
A former prime minister, he is one of the most controversial figures in Afghanistan's modern history.
Mr Hekmatyar's return comes more than 20 years after the Taliban forced him from Kabul in 1996.
He was one of seven anti-Soviet faction chiefs who led a large number of mujahideen fighters in the war against Soviet occupation in the 1980s.
But he is remembered mostly for his role in the bloody civil war of the 1990s, when the Hezb-e-Islami clashed violently with other mujahideen factions in the struggle for control of Kabul.
The Hezb-e-Islami was blamed for much of the terrible death and destruction of that period, which led many ordinary Afghans to welcome the emergence of the Taliban.
The civil war also led to Mr Hekmatyar's fall from grace - he and his men were forced to flee Kabul when the Taliban swept into power.
Another player vying for power? - By Secunder Kermani, BBC News, Kabul
Gulbuddin Hekmatyar was once known as the "Butcher of Kabul" - and was nicknamed "Rocketyar", in reference to the hundreds of rockets he rained down on Kabul in the country's civil war in the 1990s. Many in the city still haven't forgiven him.
His critics say he has long ceased to be a significant military force, and that the Taliban are unlikely to listen to his calls to take part in peace negotiations - especially whilst they feel they have the Afghan government on the back foot. His opponents also worry he will become yet another political player vying for power in the country.
But the peace deal is a success for the government, and has been welcomed by the US. The hope is Mr Hekmatyar could influence Taliban commanders who once operated under his banner and show the group that a peaceful solution to the conflict is possible.
In 2003, the US state department listed him as a terrorist, accusing him of taking part in and supporting attacks by al-Qaeda and the Taliban.
But Hezb-e-Islami has not played much of a role in the conflict in recent years, and in September 2016 the Afghan government signed a deal granting Mr Hekmatyar immunity and the release of prisoners in return for peace.
Hezb-e-Islami has supporters across the country and there are hopes that the peace agreement may encourage some Taliban leaders to consider joining the process.
But others are wary. One paper has accused him of "speaking in a bullying tone" and calling for a more centralised government that would entrench the "dominance of one ethnic group".
Mr Hekmatyar is Pashtun, as is Mr Ghani. But ethnic Tajiks, who back Chief Executive Abdullah Abdullah - Mr Ghani's former presidential rival and now partner in the national unity government, and the mainly Shia Hazaras - could see the warlord's return as a worrying sign.
In Kabul, one man told Reuter's news agency that Mr Hekmatyar's return was "a moment of pride for the country" and he hoped it would bring peace.
But another said the move would not help. "If the government really wants to bring peace to Afghanistan, they should make a peace deal with the Taliban and Daesh [so-called Islamic State], because Hekmatyar doesn't have enough supporters and his reputation among people is low."