Zimbabwe President Robert Mugabe is seen at opening ceremony of 28th summit of SADC heads of state and government in Sandton, South Africa, 16 Aug 2008

Negotiators suggest they are close to reaching a power sharing deal between Zimbabwe's president and the leading opposition group.

Zimbabwean President Robert Mugabe and opposition leader Morgan Tsvangirai both attended the opening of a regional summit in South Africa Saturday where they face rising pressure to conclude an agreement.

At least 2,000 demonstrators marched in Johannesburg to protest Mr. Mugabe.

Zimbabwe's protracted political crisis is high on the agenda for the 14-nation Southern African Development Community summit.

Sources close to the negotiations suggest an agreement is possible.  

South Africa's president, Thabo Mbeki, who has been a mediator at power sharing talks, told the Associated Press the factions are close to an agreement.

But an official with Tsvangirai's Movement for Democratic Change, Tendai Biti, said the chances of an agreement before the summit wraps up were "50-50."

Botswanan President Ian Khama is boycotting the meeting because of Mr. Mugabe's presence.

Botswana does not recognize Mr. Mugabe's election and the boycott highlights increasing pressure from African nations on Mr. Mugabe's ZANU-PF party and opposition groups to reach an agreement.

Arthur Mutambara, leader of a second opposition group in Zimbabwe, is attending the meeting.

Earlier this week, three marathon sessions failed to produce a power sharing deal.

Mr. Mugabe was declared the winner of a June 27 runoff election that many international observers dismissed as a sham.  Opposition leader Tsvangirai pulled out of the election, citing state-sponsored attacks against his supporters.

Some information for this report was provided by AFP, AP and Reuters.