Deputy Secretary of State Robert Zoellick was dispatched to Africa on Monday to push for a peace agreement to end political and ethnic conflict in the Darfur region of Sudan.

Zoellick's trip was announced after the first day of a two-day extended deadline for a settlement ended without a pact. Sudan's government has said it will accept the accord, but rebel groups are still pressing additional demands.

Disarming militias and integrating them into an armed force are among a handful of matters that must be resolved before completion of a historic deal. Sunday's deadline was extended at U.S. request.

"We are down to a few difficult issues," State Department spokesman Sean McCormack said in announcing Zoellick's mission to the talks supervised by the African Union in Abuja, Nigeria. "Nothing is done until everything is done," he said shortly before Zoellick's plane took off.

By some estimates, at least 200,000 people have been killed and 2 million driven from their homes since 2003 in the western Sudan province. After a slow start, the world's attention has focused on the conflict between a rebel insurgency and tribal militias linked to an Arab-dominated Khartoum government.

Thousands of people, some clutching signs that read, "Never Again," rallied Sunday in Washington and several of the speakers urged President Bush to take stronger action to end the suffering amid what the administration has determined was genocide.

"You need the participation and public good will of all states who have an interest in seeing that this humanitarian situation, that this tragedy is corrected," McCormack said.

Zoellick is "results-oriented" and prepared to meet with whomever can help get the agreement over the goal line, McCormack said.

The deputy secretary will be there "into the undetermined future," McCormack said.

Besides Zoellick's trip, the U.S. has been working with officials of NATO, which Washington wants to provide more logistical and training support for African Union peacekeepers.

Efforts are also under way to provide a possible United Nations force to aid African Union troops, a move the Sudanese government has said it would support if a peace treaty is signed.

In the Sudanese capital, the country's chief negotiator, Majzoub Khalifa, said the rebels' reluctance to sign the agreement was "regrettable," but that the government would begin immediately abiding by the agreement.

The African Union must decide what to do if the talks fail, Khalifa said.