WASHINGTON — America has invited the Darfur rebel leader who agreed to peace with Sudan to visit Washington amid signs the American-brokered accord is in danger of unraveling because of infighting and violence against civilians.

Minni Arkou Minnawi, leader of one of two feuding factions within the Sudan Liberation Movement/Army that has warred with the central government in Khartoum, will visit later this month for about a week, a State Department official who asked not to be identified said. The discussions with American officials will explore how to get other rebels to sign the accord.

Among rebel leaders in Darfur, only Mr. Minnawi was persuaded by an American negotiator, Robert Zoellick, to support the power-sharing agreement in May. Now Mr. Minnawi is facing rising opposition to his leadership among commanders in northern Darfur, including those from his Zaghawa ethnic group, according to the United Nations.

The three-year conflict has killed tens of thousands of civilians and forced about 2.5 million from their homes in what the United Nations calls the world’s worst humanitarian crisis. America has accused Sudan’s government of committing genocide in Darfur.

A report issued this week by the U.N. mission in Sudan cited allegations by internally displaced Sudanese that Mr. Minnawi’s faction “was indiscriminately killing, raping women and abducting” civilians.

And the United Nations’ top envoy to Sudan, Jan Pronk, said July 6 that the peace agreement is in jeopardy of collapse and violence is worsening due to clashes among rebel factions and increased attacks on civilians by pro-government militias.

The agreement is part of an effort to stop the bloodshed. America also considers crucial the transformation of a 7,000-person African Union force patrolling Darfur into a 15,000-member U.N. military mission. “I speak frequently with my secretary of state on this issue to make sure that we expedite the arrival of augmented troops to save lives,” President Bush said on July 6.

While President al-Bashir of Sudan opposes the insertion of U.N. troops, negotiations are continuing in an attempt to change his mind.

The State Department official said Mr. Minnawi’s itinerary was still being determined, including whether he would confer with Mr.Bush at the White House. A National Security Council spokesman, Frederick Jones, said late Monday that he had nothing to announce about the president’s schedule.

Colin Thomas-Jensen, advocacy and research officer for Africa in the Washington office of the International Crisis Group, a policy research organization, said Mr. Minnawi’s weakening position is undermining the accord.

“The U.S. does find itself in a difficult situation because it trumpeted this agreement as the solution, as the way forward for Darfur,” Mr. Thomas-Jensen said. “However, what most people agree is the way forward is the U.N. peacekeeping force.”

To entice Mr. Minnawi to sign the Darfur agreement, Mr. Bush promised the rebel chief in a personal letter that America “will strongly support implementation of the peace accord” and will insist that any party not cooperating “be held accountable by the U.N. Security Council.”

Mr. Minnawi’s rival who refused to sign the accord is Abdel Wahid Mohamed el-Nur, who has support among the Fur people, the largest ethnic group in Darfur. He was joined by a smaller rebel group, the Justice and Equality Movement.