The United States demanded an emergency meeting of the United Nations Security Council on Thursday over a letter in which Sudan's government said it would view any troop commitments to a future peacekeeping force in Darfur as a "hostile act."

The unsigned letter addressed to several UN missions, dated Oct. 3, also said troop commitments would be seen as a "prelude to an invasion."

In the letter, Sudan reiterated that it rejects a Security Council resolution passed in August that would seek to give the UN authority over an African Union peacekeeping mission that has been unable to stem the violence in the Sudanese region of Darfur.

The letter refers to a note sent by the UN asking nations to nominate police personnel for an unspecified force.

"In the absence of Sudan's consent to the deployment of UN troops, any volunteering to provide peacekeeping troops to Darfur will be considered as a hostile act, a prelude to an invasion of a member country of the UN," the Sudanese letter said.

U.S. wants response from UN

U.S. mission spokesman Richard Grenell said the United States wants the Security Council to discuss the letter in an emergency session Thursday and approve a statement addressing it.

Grenell characterized the letter as "the latest Sudanese obstruction of a UN peacekeeping mission in Darfur."

More than 200,000 people have been killed and 2.5 million displaced as a result of fighting between rebels and government-backed militias in Darfur since 2003.

Sudanese President Omar al-Bashir has so far refused to allow the United Nations to take over the largely ineffective African Union peacekeeping force in Darfur, a roadblock that rights groups say is only exacerbating the violence.

The letter did, however, repeat previous Sudanese claims that the government would allow the UN to help support the African Union peacekeepers.

That was reiterated out of Khartoum on Thursday, when the official Sudan News Agency reported that al-Bashir had sent UN Secretary General Kofi Annan a message welcoming the assistance.

He said that help would enable the African Union force to "carry out its most recent mission and duties," the agency reported.

"Co-operation and consultations between the United Nations, the African Union and the Government of National Unity would speed up finding a solution to the question [of Darfur] and help instil a permanent peace in Sudan," al-Bashir said in his message, according to the news agency report.

Aid not alternative to troops

But a UN spokeswoman said the provision of funds and logistics did not mean the world body was backing off from its plan to put the Darfur mission under UN control.

Radhia Achouri, spokeswoman for the world body in Sudan, said the aid offer "is not to be seen as an alternative to a UN deployment" in Darfur.

Earlier this week, U.S. President George W. Bush said the United Nations should not wait any longer to approve a force for Darfur.

David Triesman, the British Foreign Office's minister for Africa, said in September the international community must consider all options — including military intervention — as it mulls how to deal with Sudan's rejection of the UN peacekeeping force.