The Sudanese government has been accused of violating a UN arms embargo by flying weapons into Darfur in breach of UN Security Council resolutions.
At least 2.4 million people have been displaced by the Darfur conflict
A UN report says Sudan painted aircraft white to make them look like UN planes.
Sudan's envoy to the UN, Abdel Mahmood Abdel Haleem, said the allegations were "a lie" and that military assets were simply being moved around the country.
The US and the UK will later begin talks with other Security Council members on a new resolution on Darfur.
Abdel Mahmood Abdel Haleem told the BBC: "According to the comprehensive peace agreement signed [after the civil war in the South] between the Sudan government and the SPLM, we have to move our military assets and aircraft and all assets from the South to other regions in the country.
UN DARFUR PLAN
Phase 1 - UN financial backing for AU mission
Phase 2 - UN sends logistical and military support
Phase 3 - UN takes joint command of hybrid force
"We are moving these military assets to their respective places. We are not using these aircraft for any military function in Darfur."
But a New York Times journalist who has seen a leaked copy of the UN report says there is no doubt about the evidence.
"One thing is pictures that appeared with the report that we actually published in the New York Times today," Warren Hoge told the BBC World Service's World Today programme.
"There are very clear pictures of planes painted white, and also with the UN designation on the left-hand wing of one of the planes. And also a good deal of testimony from the investigators who compiled the report.
"It's the credibility of the United Nations versus the credibility of the Sudanese authorities - and I think on that basis the United Nations report looks pretty good."
The report was compiled by a five-person panel for the Security Council committee monitoring sanctions against Sudan.
US sanctions warning
US Deputy Secretary of State John Negroponte ended his tour of Sudan and its neighbours on Wednesday, without meeting Libyan leader Muammar Gaddafi.
Mr Negroponte visited Sudan, Libya, Chad and Mauritania, hoping to increase pressure on Sudan to let more UN peacekeepers into Darfur.
President George W Bush has said he wants tougher sanctions if Khartoum did not accept 20,000 UN peacekeepers being sent to the region, a move opposed by Russia and China.
Mr Bush said he was giving UN Secretary General Ban Ki-moon one last chance to reach a diplomatic solution.
Sudan said earlier this week it would allow 3,000 UN troops into Darfur to support 7,000 African Union troops, but has not agreed to a much larger force.
The four-year Darfur conflict between rebels and pro-government Arab militia has seen more than 200,000 deaths and at least 2.4 million displaced.