Sudan's government has rejected new allegations that it is giving direct support and orders to the Janjaweed Arab militia in the Darfur region.
The Janjaweed are accused of 'ethnic cleansing'
A Sudanese Foreign Ministry spokesman told the BBC his government was instead working hard to try to disarm them.
Earlier, a UK asylum seeker known as Ali, who said he was in the Janjaweed, told the BBC he saw ministers giving orders at their training camps.
Ali said he took part in village raids after bombings by Sudan's air force.
He said the majority of casualties were civilians and that he had witnessed Janjaweed fighters raping women.
Khartoum has always denied any links to the Janjaweed, who have been accused of war crimes against civilians in Darfur.
More than two million people have fled their homes during the three-year conflict and more than 200,000 are estimated to have died.
Sudanese government spokesman Ali al-Sadek told the BBC's Arabic Service that he believed the former Janjaweed fighter made his allegations on the BBC television programme Newsnight because he is claiming political asylum in the UK.
"I think this is a pretext that weakens everything he alleged," Mr Sadek said.
The spokesman also said the interior minister mentioned by Ali was not Abdul Rahim Muhammad Hussein - although Mr Hussein held the post until 2005.
Mr Al-Sadek reiterated the Sudanese government's denial of aiding any militias in Darfur, adding that the government was cooperating with the United Nations.
"We are seeking to seize the weapons of this bandit militia. We are exerting efforts alongside the UN and many other organisations in order to establish security and peace."
The former fighter, Ali, said the men who had trained them were wearing the uniforms of the Sudanese military, adding that Mr Hussein was a "regular visitor".
"The Janjaweed don't make decisions. The orders always come from the government," he said.
"They gave us orders, and they say that after we are trained they will give us guns and ammunition."
Hilary Benn, a British government minister who visited Darfur on Monday, said the man's evidence was "clearly very serious".
Mr Benn urged him to speak to investigators from the International Criminal Court.
Meanwhile the Aegis Trust, which campaigns against genocide, has revealed details of a letter it believes is genuine and it says provides evidence of a systematic campaign to drive Africans from Darfur.
The US State Department is reported to have considerable doubts about its authenticity.
The copy of the letter, which has been seen by the BBC, is dated 16 August 2004 and is translated from Arabic.
Aegis Trust say they obtained it from a US Marines captain serving as an adviser to the African Union mission in Darfur.
It is signed by a Janjaweed commander and describes orders from Sudan's president to "change the demography of Darfur".
"We confirm that directives have been issued - to change the demography of Darfur and make it void of tribes of African origin - to kill, burn all farms, confiscate the belongings of tribes of African origin, forcibly displace them from Darfur, and kill their intellectuals and the youth, because they can join the fight with the rebels," the letter says.