Sudan is arming civilians in South Kordofan as fighting against rebels in the state that borders South Sudan intensifies, the BBC has found.
Men in Talodi town told the BBC that as supporters of President Omar al-Bashir they were given arms to help the army.
A rights group also told the BBC it had concerns that such untrained fighters were committing human rights abuses.
Meanwhile, the International Rescue Committee says a new wave of refugees has fled South Kordofan to South Sudan.
The aid agency said as many as 400 people were arriving every day at Yida camp, 25km (15 miles) inside South Sudan, up from an average of 50 a day a week earlier.
South Kordofan is one of three areas in Sudan hit by conflict since South Sudan became independent in July.
The disputed oilfield of Heglig is also in South Kordofan and was captured by South Sudanese forces this week.
On Friday, Juba outlined circumstances under which undefined : an assurance that Heglig will not be used as a base for cross-border raids and the deployment of UN troops.
The fighting in South Kordofan has escalated recently since several Darfuri rebel groups joined forces with SPLM-North to form the Sudan Revolutionary Front, which has claimed responsibility for several joint attacks.
The BBC's James Copnall visited Talodi, an area which has been badly affected by clashes with the rebels. He also found evidence of civilians being armed.
"The government gave us the guns. Omar al-Bashir gave us the guns," says Hissein Ahmed Sharif, one of a group of men in Talodi market during our correspondent's visit.
They are from the Awlad Shoron group - perceived to support President Bashir. Many in the local Nuba community sided with southerners during the long civil war, which ended in 2005 and eventually led to South Sudan seceding.
"We are Arabs," Mr Sharif said, adding that the attackers were Nuba or "Tora Bora", which is slang for the Darfur rebels.
"I am not soldier, I am just helping the army. I don't get a salary," he said.
He and his comrades had been given 87 guns, but this was not enough as the rebels had heavy weapons including artillery, he said.
Our reporter says the governor of South Kordofan, Ahmed Haroun - wanted by the International Criminal Court for alleged war crimes in Darfur - is one of many Sudanese officials who accuse South Sudan of providing the rebels with their arms. South Sudan denies the charge.
Arming civilians is not a new practice in Sudan, but it is usually done as part of the Popular Defence Forces, a paramilitary organisation, our correspondent says.
President Bashir has recently ordered each of Sudan's 15 states set up a camp for new recruits to the PDF.
Hafiz Muhamed, from the rights group Justice Africa Sudan, says more and more civilians are being armed in South Kordofan and elsewhere in Sudan.
"The army has a serious problem, a shortage of manpower," he told the BBC.
"These groups that are mainly armed civilians, they pretend they are protecting their area, but they commit a lot of violence and looting."
"Many are in the Popular Defence Forces. They are not a disciplined army so there is a risk of committing abuses."
Our reporter says the paramilitary PDF were accused of many atrocities during the civil war and have been accused of abuses in Darfur, and SPLM-North also says the PDF have committed massacres in South Kordofan in the last year.
Now they are fighting against SPLM-North - and committing abuses, according to SPLM-North's Secretary-General Yasir Arman.
"They use these militias to implement their scorched earth policy," Yasir Arman told the BBC, in a Skype interview from an undisclosed location.
"Last week in Abu Hassan and Toma, villages were burnt down and people killed, and it has happened in many places in the Nuba mountains."
Armed and partially trained paramilitaries are an integral part of Sudanese military strategy and the country's current foreign minister, Ali Karti, used to lead the PDF, our reporter says.
A state minister in Southern Kordofan, Ibrahim Abdallah Abdel Karim, told the BBC his government had no choice other than to arm civilians.
"This is national," he said. "If a person is put in a position that he will be killed, then he will defend himself, by all means."
Our reporter says it is not just a Sudanese phenomenon as South Sudan's President, Salva Kiir, suggested on Thursday that many armed civilians in his country should mobilise if necessary to fight against Sudan.