NEW YORK, Jul 24 (OneWorld) - A leading U.S.-based humanitarian group is urging the George W. Bush administration to engage all rebel groups in the Darfur peace process as the U.S. president prepares to talk with the leader of just one particular faction.

Bush is expected to meet one of the rebel leaders on Tuesday, apparently in appreciation of his decision to sign a peace deal reached with the government in Khartoum some two months ago.

But despite signing the peace agreement in May, faction leader Minni Minawi's forces remain involved in violence, according to U.S. activists who are engaged in humanitarian work in the region.

Though Minawi has denied allegations of violence, says Refugees International, a Washington, DC-based group, a vast number of displaced Darfuris have reported that his forces are responsible for ongoing attacks against civilians.

The group says since the signing of the peace agreement there has been no let up in violence in northern Darfur, where the refugee population has increased--in one camp alone by 10 percent, or more than 3,500 people.

"Please stress that he (Minawi) must honor the terms of the Darfur Peace Agreement," said Kenneth Bacon, president of Refugees International, in a letter addressed to President Bush.

Bacon, who is currently visiting the region, urged the U.S. president to also reach out to other rebel leaders, including the Abdel Wahid faction of the Sudanese Liberation Army, and convince them to sign the peace agreement.

"Although Minawi is the dominant military leader among the rebels," Bacon said, "he represents a small tribe and is intensely disliked by the dominant tribe, the Fur."

Bacon fears that a strong association with one group could weaken U.S. influence with other groups, just as the African Union forces have been discredited by their embrace of Minawi.

"It is important that the U.S. find ways to reach out to other groups and leaders as it fetes Minawi in Washington," he said. "The U.S. should not support parties that are continuing to fight after signing the peace agreement."

The conflict between the Janjaweed militias backed by the Sudanese government and rebel groups that began in 2003 has claimed tens of thousands of innocent lives in addition to forcing more than two million people to flee their homes.

While the Janjaweed remain a menacing force elsewhere in Darfur, Refugees International suggests that Minawi's troops pose the biggest threat to security in the northern region.

Though the 7,000-strong African Union (AU) forces have helped bring some stability in the region, like many others, the group believes that they do not have the capacity to carry out all the tasks to ensure peace without the direct involvement of the United Nations.

But the proposed presence of a UN-led force in Sudan has so far been rejected by the government in Khartoum.

The AU force, according to Refugees International, "is too small, too weak, and too discredited to continue" its operations. Also, it continues to lack financial resources and there is no sign that it will receive any in the near future.

Many other international humanitarian aid and advocacy groups agree.

In a statement released last week, Washington, DC-based Africa Action called on the U.S. government and the United Nations to do more--both diplomatically and logistically--to ensure the speedy deployment of UN forces in Darfur.

The UN should "immediately provide the African Union troops already on the ground with a...mandate to protect civilians, turning them into a 'blue-helmeted' UN force," the group said, adding that those forces should then be reinforced with UN peacekeepers to comprise at least 20,000 troops.

Africa Action also called on U.S. officials to use their leverage with both Khartoum and dissenting members of the UN Security Council--particularly Russia and China--to help expedite the process of putting UN forces on the ground.

In a separate statement last week, eight of the largest international aid groups, including Christian Aid, the International Rescue Committee, and Islamic Relief, warned that the AU force was "chronically under-funded and unable to do its vital job."

The coalition called on the world's wealthier nations to provide $270 million to cover the mission's urgent peacekeeping needs--including food, medical care, salaries of personnel, vehicles, night-vision goggles, and armored personnel carriers--through December.

In his letter, Bacon suggested that the administration should "push the AU and the UN to begin a broad Darfur-Darfur dialogue" to include all parties in the process of reconciliation and rebuilding, including women and youth leaders.

"Achieving peace in Darfur will not be easy under any circumstances," said Bacon. "The Peace Agreement is an imperfect start, but it is a start."

Meanwhile, UN officials from the region report that the ongoing violence is hindering their efforts to provide humanitarian assistance to those in dire need of food and medicines.

"Direct attacks against humanitarian workers, acts of banditry, and fighting among rebel groups mean the UN has access to less than 80 percent of beneficiaries," said a statement from the UN mission in Sudan Monday.

UN officials said they are worried that the security conditions inside some camps for internally displaced people "are so poor" that humanitarian operations there have been placed at risk.

In Zam Zam camp in northern Darfur, the presence of arms belonging to elements of the Sudan Liberation Army is raising concerns, they said, adding that last Thursday three government workers and police officers were killed at Zelengi camp in the western region.

The reports come as Secretary-General Kofi Annan's special envoy Jan Pronk completed a two-day tour of south Darfur as part of his regular visits to the three states in the region.