In a report, to be submitted to the African Union's (AU) Peace and Security Council on Thursday, Alpha Oumar Konare, the AU Commission chairman said the Sudanese troops were painting their vehicles white, the colour of AU peacekeepers' vehicles "to disguise their identities and launch surprise attacks on their opponents."
Konare said this new development threatened to undermine the credibility of (the African Union peacekeeping mission) and could draw the mission into the conflict.
He said three government vehicles and a helicopter gunship had been spotted painted white.
"The government should ensure that no white coloured vehicles are used for military operations. The government should stop using white aircraft and vehicles for any security related activity", he said.
The allegations come as Sudan prepares to host the AU summit on 23-24 January, and under normal protocol would then take over the next rotating chairmanship of the 53-nation body.
The prospect of Sudan taking over the position has caused unease among many in the continent.
One of the problems is lack of clarity on AU rules - the host usually becomes chairman, but that is not cast in stone.
The AU must draw up clear criteria
for its chairmanship
Siphamandla Zondi, Africa director at Johannesburg think-tank, Institute for Global Dialogue, said: "The appropriate thing would be for the AU to draw up criteria for the chairmanship, which is supposed to be an example of what the AU is all about, especially at a time when Africa is trying to find its space on the global stage."
Neighbouring African countries see Sudan as poor ambassador for Africa and fear that seeing it take up the AU chair would sink the Darfur peace process.
They hope the continent's big diplomatic players - like South Africa and Nigeria - find a more suitable candidate.
David Mozersky, a Nairobi based Sudan expert, told Reuters: "If Sudan takes the AU leadership, it wins credibility, but to the detriment of the African Union. The Sudan government has been one of the worst perpetrators of human rights abuses on the African continent for the last two years."
"The Sudan government has been one of the worst perpetrators of human rights abuses on the African continent for the last two years"
To date neighbouring Chad's President Idriss Deby - who accuses Sudan of backing rebels seeking to overthrow him - is the only African head of state openly campaigning against Khartoum.
Deby, who wants Nigeria to continue holding the AU chairmanship, said: "An aggressive neighbour like Sudan is not capable of hosting the next AU summit, not to mention being the next chairman."
Crimes against humanity
Khartoum is accused of backing militia known as Janjawid in a campaign of rape and killing of Darfur civilians that Washington has termed genocide. Rights groups are also outraged at the prospect of Sudan chairing the AU.
Peter Takirambudde, Africa director of US-based Human Rights Watch, said: "The African Union should not reward the sponsors of crimes against humanity.
"How can the African Union be seen as a credible mediator in Darfur if one of the warring parties hosts its summit and becomes the head of the organisation, as well?"
|The Darfur issue must be resolved|
before Sudan can host the summit
For its part the Sudanese government is keeping a low profile on the issue.
It denies sponsoring violence in Darfur and says last year's historic north-south peace accord demonstrate its credentials.
Mutrif Siddig, Sudan's foreign ministry under-secretary told Reuters: "We are going to leave it to the presidents to decide if they will give us this opportunity.
Chad's neighbours recognise the awkwardness of a Sudan chairmanship but are avoiding a hard-line public stance.
Cosme Arouna, Benin's foreign ministry spokesman, said: "Chad's opposition (to Sudan hosting the AU summit) is a non-starter - it's not right to be dictating to the other states.
"As long as the Darfur problem is not completely resolved, Sudan does not seem to me to be well placed to preside over the destiny of the AU."