Special envoy Lakhdar Brahimi and Hedi Annabi, the head of U.N. peacekeeping, hope Khartoum will respect a Security Council resolution for a U.N. force to take over peacekeeping from an under-equipped African Union mission, a spokesman said.
"The overall aim of the visit is to discuss the implementation of the Darfur peace agreement and speed up the arrival of a U.N. peacekeeping force," U.N. spokesman Bahar Elkoussy said.
Brahimi and Annabi are scheduled to meet President Omar al-Bashir and Sudanese legislators during their four-day visit, Elkoussy said.
Elkoussy said the envoys' first task would be trying to persuade the government to grant visas to a U.N. assessment team that would prepare for the transfer of the African Union peacekeeping mission to the U.N. force.
He said he did not know when the evaluation team would arrive.
"It all depends on the Sudanese government," Elkoussy said, adding that the U.N. was optimistic that Khartoum would respect the Security Council resolution.
The U.N. delegation arrived a day after Secretary-General Kofi Annan reported that Khartoum was violating international humanitarian law by barring fuel, food and relief aid to civilians in Darfur.
The Sudanese government long has resisted a U.N. peacekeeping force in Darfur, arguing that an African problem should be handled by African troops. While it did say it would accept a U.N. force once a peace agreement was signed, it responded coolly to the Security Council resolution last week.
The resolution provides for the U.N. force to take over peacekeeping from the African Union, which has been unable to stop the violence in the western region where a three-year rebellion and counterinsurgency has cost more than 180,000 lives and caused the displacement of 2.5 million people.
The government and the biggest rebel group in Darfur signed a peace agreement May 5 that called for a cease-fire within 72 hours and the eventual disarmament of all militia. But the cease-fire was ignored and scores have been killed in subsequent fighting involving government troops and various armed groups.
Annan's report to the Security Council said the people of Darfur had been exposed to increased violence in recent months and aid groups had cut back their relief programs because of insufficient funding.
A former Algerian foreign minister, Brahimi is a widely experienced U.N. troubleshooter who has been a special envoy in Afghanistan and Iraq.