RIYADH, Saudi Arabia - UN Secretary-General Ban Ki-moon and Sudan's president reached an agreement to work out UN support for African peacekeepers in the war-torn region of Darfur and to boost the beleaguered peace accord, the Arab League said Thursday.

But it appeared UN chief Ban Ki-moon was unable to win President Omar al-Bashir's acceptance of a UN force in Darfur during talks on the sidelines of an Arab League summit in the Saudi capital.

Hours before the meeting, al-Bashir sharply rejected any UN deployment in a speech to the summit, repeating his stance that the UN role must be limited to logistical and financial help for African Union peacekeepers in Darfur.

The UN and Sudan reached an agreement in November that called for a joint UN-African Union force of some 20,000 peacekeepers, but al-Bashir has since backed off the deal, saying he would only allow a larger AU force.

The undermanned and underequipped 7,000-strong AU force in Darfur has been unable to stop the violence, where more than 200,000 people have been killed in nearly four years of fighting between the government and ethnic African rebels.

The violence has only increased since a peace deal was signed last year by the government and one rebel group in Abuja, Nigeria. Other rebel groups rejected the deal and continued fighting.

During the Riyadh talks, Ban and al-Bashir agreed to practical measures to reduce obstacles in the implementation of the Abuja peace deal and the later UN-Sudan deal, the Arab League said in a statement Thursday.

The sides agreed to "define the size of the African forces and their weaponry as well as the logistical and technical support, supervision, financing and the ways of participation by the United Nations," it said.

They also agreed to work to "bring groups that have not signed the Abuja accord into the political process to speed up national reconciliation."

On Thursday, US and other officials called for an investigation into a gunbattle between government forces and former rebels from the Sudan Liberation Movement that killed 10 people last week in the Sudanese capital of Khartoum.

The violence, which further jeopardized an already weak peace agreement, was especially troubling because SLM leader Minni Minawi was the sole rebel chief to sign the Abuja peace deal.

The international community has struggled for months to win al-Bashir's acceptance of the UN force. A Security Council resolution calls for a UN force, but only with Khartoum's consent.

Al-Bashir's government is accused of backing Arab militiamen blamed for widespread atrocities against ethnic African civilians. More than 2.5 million people have been driven from their homes in the large, barren region of western Sudan.

In his speech to the Arab summit on Wednesday, al-Bashir slammed UN resolutions calling for UN troop deployment in Darfur saying they "provoke the conflict in Darfur, instead of finding a solution for it."