Johannesburg - Opening a regional summit on the political crisis in Zimbabwe South African President Kgalema Motlanthe expressed disappointment at the impasse in powersharing talks between President Robert Mugabe and the opposition and urged them to quickly reach agreement.

Mugabe and opposition leader Morgan Tsvangirai are attending the meeting of the 15-nation Southern African Development Community (SADC) in Johannesburg.

The conflict in the eastern Democratic Republic of Congo, a member of SADC, is also on the agenda of the meeting, which Congolese President Joseph Kabila is attending.

Motlanthe, whose country holds the rotating SADC chair, called for "an immediate ceasefire" to allow the delivery of humanitarian assistance to refugees displaced by the fighting and urged the parties to the conflict to pursue a political solution.

SADC was "encouraged" by the diplomatic interaction between the Congo and neighbouring Rwanda, which has been implicated in the conflict, he said.

Motlanthe also called for the overstretched UN peacekeeping force in Congo, MONUC, to be given more powers.

"Their current mandate limits their ability to be real peacemakers," he said.

Sunday's summit is seen as the last chance to save Zimbabwe's September 15 power-sharing agreement from collapse.

SADC members have warned they will take a tough line at the summit with Mugabe and Movement for Democratic Change (MDC) leader Tsvangirai, who have been bickering for two months over the make-up of the unity government they agreed to on September 15. MDC minority faction leader Arthur Mutambara, the third party to the agreement, is also attending the summit.

Motlanthe called on the three parties "to build on achievements made thus far and reach agreement on outstanding issues, including the ministry of Home Affairs."

September's "historic agreement" was still "the only vehicle to extricate Zimbabwe" from the challenges facing the country, Motlanthe said.

According to the terms of the deal, Mugabe remains president and Tsvangirai becomes prime minister of a unity government of 31 ministries.

The MDC has accused Mugabe's Zanu-PF of trying to hold onto the important ministries. The debate over who controls home affairs has been particularly acrimonious.

The MDC has agreed to let Zanu-PF retain defence in return for home affairs, which controls the police and the electoral machine. Zanu-PF is insisting on retaining it.

In the run-up to Sunday's summit the two parties were continuing to blame each other for the failure to put in place a government and making noises about pulling out of the deal.

Observers say a power-sharing government is the only way of ending Zimbabwe's nearly decade-long economic slide, which has intensified sharply in recent months.

Some 3 million people in the once model African economy now require food aid. (dpa)