Senior US politician Bill Richardson has held talks with Sudan's president to try and persuade him to accept more UN troops in war-torn Darfur.
More than two million people have been displaced by the conflict
Mr Richardson, a former US ambassador to the UN, is seen as enjoying better relations with President Omar el-Bashir than most US politicians.
He said some progress had been made and they would meet again on Wednesday.
Mr Bashir has always resisted plans for the UN to take over peacekeeping efforts in Darfur.
Meanwhile, US envoy to Sudan Andrew Natsios is travelling to China, which has played a key role in preventing condemnation of Sudan at the UN Security Council.
China has strong trade ties to Sudan.
The US says government-backed Arab militias are carrying out a genocide of black Africans in Darfur, where more than two million people have fled their homes.
At least 200,000 people have died in Darfur in the past four years.
Sudan says the problems in Darfur are being exaggerated.
Before meeting President Bashir, Mr Richardson said he hoped to convince Sudan to accept UN forces in Darfur as soon as possible.
"I have to tell you, my record with Bashir is pretty good," he told international aid workers in the capital, Khartoum, reports the AP news agency.
AP reports that some aid workers are sceptical about whether Mr Richardson's mission can succeed.
Last year, Mr Richardson negotiated the release of a US journalist accused of spying after meeting Sudan's leader.
The New Mexico state governor, seen as a possible Democrat presidential candidate in 2008, is due to visit Darfur on Tuesday.
The UN wants to strengthen peacekeeping troops but there is conflict with Sudan over the number of UN soldiers to be deployed there.
Some 7,000 African Union troops have not been able to prevent the conflict worsening.
A peace agreement was signed last May between the government and one leading rebel group but violence has continued, with rival rebels refusing to sign.
The UN has a three-part plan to strengthen the current 7,000-strong African Union force with UN troops.
Mr Bashir has consistently opposed any large UN deployment although he has indicated he wants to support the UN's plans.
The Darfur conflict began in 2003 after a rebel group began attacking government targets, saying the region was being neglected by Khartoum.
The rebels say the government is oppressing black Africans in favour of Arabs.