UNITED NATIONS - Sudan's president is sending a letter to Secretary-General Ban Ki-moon expressing his commitment to the deployment of several thousand U.N. peacekeepers to help end the violence in Darfur, Sudan's U.N. envoy said Friday.

The deployment would be the second step of a three-stage U.N. plan that would culminate in a 22,000-strong joint UN-African Union peacekeeping mission.

Sudanese President Omar al-Bashir has given conflicting signals about his commitment to the plan, and Ban asked him earlier this year to state his acceptance of the second phase in writing.

Al-Bashir's letter expresses his commitment but also raises "issues of operational, technical and legal aspects" of the proposal, Sudanese Ambassador Abdalmahmood Abdalhaleem told The Associated Press. He declined to elaborate.

Sudan agreed to the initiative in November. Al-Bashir reiterated his commitment in a Dec. 23 letter to former U.N. Secretary-General Kofi Annan. But last month, al-Bashir said U.N. troops were not required in Darfur because the 7,000-member AU force on the ground could maintain order. The Sudanese president has insisted the AU force needs only technical and financial support from the U.N.

Abdalhaleem said Ban would be receiving the letter "at any moment." Ban's office said the secretary-general did not have the letter but was told al-Bashir had written it.

"Sudan of course is committed to the support by the U.N. to AMIS," Abdalhaleem said, referring to the AU force by its acronym.

On Friday, the U.S. State Department called on both Sudan and the United Nations to speed up the deployment of the full joint AU-UN force.

Spokesman Sean McCormack issued the appeal as U.S presidential envoy Andrew Natsios arrived in Sudan's capital, Khartoum, for a 10-day visit that will include stops in the western Darfur region and southern Sudan.

"We are pushing on the Sudanese -- we as well as others -- to make sure that those forces are able to deploy in the areas that they need to deploy to and push on the Sudanese to do everything that they can to stop the violence," McCormack said.

McCormack said the U.S. administration is not satisfied with the yearlong U.N. time frame for the deployment and that not enough countries are pledging troops for the mission.

"The timeline needs to be reduced," McCormack said. "This is too critical a humanitarian issue."

The first phase -- a "light support" package adding some equipment, military officers and U.N. police to the AU operation -- is nearly almost complete. The second phase is a "heavy support" package that includes the deployment of more than 3,000 U.N. military, police and civilian personnel.

Darfur's conflict erupted in 2003 when ethnic African rebels took up arms against the Arab-dominated central government, accusing it of neglect. More than 200,000 people have died and 2.5 million have fled their homes. The government is accused of unleashing militias known as the janjaweed, which are blamed for the bulk of the conflict's atrocities.

In a report Wednesday, Ban called on al-Bashir to "uphold his commitment" to the U.N.-AU peacekeeping plan.

He also urged countries to provide "urgent contributions of human resources and equipment" for the joint force and said the second phase would cost $287.9 million.

On Friday, European Union defense ministers offered support the joint mission. However, the EU has provided most of the financing for the AU force now in Darfur -- some $530 million since 2004 -- and the bloc's special peace support fund for Africa has run dry.

EU foreign ministers are expected to seek extra funding Monday from the EU aid budget and from the coffers of its 27 member governments.