Washington - United States Deputy Secretary of State Robert Zoellick is heading to Sudan to push rebels and the government toward peace in crisis-torn Darfur amid concerns by some lawmakers and rights groups that Washington is being too soft on the Islamist leadership in Khartoum.

Zoellick's trip comes as peace talks between fractious rebel leaders and the government are stuttering, and an upsurge in violence in the western region of Darfur is drawing increasing global attention to the rising death toll and the suffering of some two million refugees.

The United States has accused the Khartoum government and allied militias of genocide in Darfur, where the violence has claimed tens of thousands of lives.

"Large-scale killing in Darfur has subsided, but a recent upswing of violence is a serious danger," Zoellick said on Friday, two days before his fourth trip to Africa's largest country since April.

'So we'll keep pushing and pushing and pushing on the peace talks'
"Darfur rebel groups are fighting among themselves. Any spark could set off a wildfire, so all of the key parties have important work to do to keep things on track," he said in a news release. Zoellick will also travel to Kenya for talks with the main rebel leaders.

Eleven months after helping forge a landmark peace deal to end a protracted war in southern Sudan, Zoellick will also prod members of the new national unity government to implement difficult but vital elements of the north-south accord, including demobilizing troops and defining internal borders.

The United States says the successful implementation of the southern Sudan peace deal is essential to convince the Darfur rebels that a similar accord will bring them the political voice and economic support they seek.

"We are committed to peace in Sudan," Jendayi Frazer, assistant secretary of State for African affairs, told reporters on Friday. "So we'll keep pushing and pushing and pushing on the peace talks."

Despite the pledges, critics - including several vocal Republican and Democratic members of Congress - have accused the US government of being too easy on Sudan, which won praise for its counter-terrorism co-operation since the September 11, 2001, attacks.

They say Washington must press Sudanese leaders harder to stop any support for the "Janjaweed" militiamen, who stand accused of a widespread campaign of rape, killing and burning in non-Arab villages during the two-and-a-half-year-old Darfur revolt.

Non-Arab rebels took up arms in early 2003, accusing the Arab-dominated central government of monopolising wealth and power and marginalising Darfur.

John Prendergast of the International Crisis Group think tank said there has been a lot of internal government debate on how to deal with Sudan, and he believed the Bush administration had softened its approach because of Sudan's value in the counter-terrorism fight.

Democratic Senators Richard Durbin and Jon Corzine, as well as Republican Senators Mike DeWine and Sam Brownback, called on President George Bush this week to request additional funds for African Union peacekeepers in Darfur, as lawmakers cut back $50-million in support for them.

"This is simply unacceptable and is a tragedy for the people of Darfur," said Reverend Richard Cizik, a vice president at the National Association of Evangelicals.

Frazer said Washington, which has provided $160m to help secure peace in Darfur, was keeping up the pressure on Sudanese President Omar al-Bashir and his government to work harder toward peace.