Leaders of key members of the U.N. Security Council and the African Union meet at U.N. headquarters on Wednesday where they are expected to debate the crises in Zimbabwe, Sudan and Somalia.

The meeting, which will be chaired by South African President Thabo Mbeki, is due to focus on Security Council cooperation with the AU and other regional organizations.

South Africa has drafted a resolution cementing this cooperation, which is expected to adopted on Wednesday.

U.N. Secretary-General Ban Ki-moon joined the United States, Britain and France on Tuesday in urging the Security Council and AU leaders to take up the worsening election standoff in Zimbabwe, despite resistance from South Africa.

Ban said the summit, which British Prime Minister Gordon Brown and several African Union leaders will attend, offered "a natural opportunity to address the situation in Zimbabwe."

Britain has accused Zimbabwean President Robert Mugabe of delaying the results of the country's March 29 election to try to subvert the outcome. Opposition leader Morgan Tsvangirai has said he won the election and accuses Mugabe of planning violence to overturn the results.

South Africa holds the Security Council's rotating presidency and has opposed council discussion of Zimbabwe, arguing that the problems there are not a crisis and do not represent a threat to international peace and security.

Pretoria's U.N. envoy Dumisani Kumalo said the issue was being dealt with by the Southern Africa Development Community, which has resisted calls for greater pressure on Mugabe.

But Ban said it was time the United Nations got involved.

"I will be engaging in a number of meetings with the leaders tomorrow to discuss what the United Nations and how the international community could help the Zimbabwean people and authorities to resolve this issue," he said.

He said Mugabe's government should release the election results "so that the Zimbabwean people will be able to enjoy the democratic process, and also they should be able to overcome these serious humanitarian difficulties."

DARFUR AND SOMALIA

The Security Council is not expected to make a unanimous statement or resolution on Zimbabwe because of resistance from South Africa and other council members. But any discussion of the issue at the meeting will increase the pressure on Mugabe, Western diplomats said.

Also to be debated is the crisis in western Sudan, where only 9,000 of the required 26,000 U.N.-AU peacekeepers have been deployed in the war-racked Darfur region.

International experts estimate around 2.5 million people have been displaced and 200,000 have died in five years of violence in Darfur which Washington calls genocide. The Khartoum government denies genocide and puts the death toll at 9,000.

Somalia's Foreign Minister Ali Ahmed Jama said on Tuesday that Somali President Abdullahi Yusuf would tell the Security Council that international peacekeepers were urgently needed to bring stability to his lawless country.

"We hope the Security Council would take meaningful steps to assume its responsibility and engage and replace the African Union force there with a U.N. force," he said. "This is the proposal we are going to make."

Talk of outside intervention is still coloured by memories of a battle in 1993 in which 18 U.S. troops and hundreds of Somali militiamen died. The incident inspired a Hollywood movie, "Black Hawk Down" and marked the beginning of the end for a combined U.S.-U.N. peacekeeping force.