South African President Thabo Mbeki and Nigerian leader Olusegun Obasanjo arrived in Harare on a delicate mission. They flew to Harare for talks with Zimbabwean President Robert Mugabe and opposition leader Morgan Tsvangirai centering on Zimbabwe's disputed presidential election.

Mr. Mugabe was sworn in for another six-year term Sunday after election officials declared him the winner by a wide margin. But Mr. Tsvangirai has refused to recognize the election results and alleges there was massive rigging by the ruling party, ZANU-PF.

The Commonwealth observer mission says the poll was so flawed by violence and intimidation that it did not reflect the will of the Zimbabwean people.

The Nigerian and South African leaders, along with Australian Prime Minister John Howard, are to meet Tuesday in London to decide whether the Commonwealth group of nations will impose sanctions on Zimbabwe, possibly including suspension from the Commonwealth.

Commonwealth nations discussed imposing sanctions on Zimbabwe at a heads-of-government meeting in Australia earlier this month. At the summit, African leaders largely lined up to support Mr. Mugabe, while industrialized nations including Britain, Canada, and Australia called for Zimbabwe's immediate suspension from the group.

After a contentious round of talks, the heavily divided group decided to delay taking any action until they had heard from their observer team after the poll.

A few days after the results were announced, the Commonwealth observers released an interim report harshly condemning the election. They said it was, in their words, conducted in a climate of fear and suspicion.

The head of the mission, former Nigerian leader Abdulsalami Abubakar, said the elections were marred by a high level of politically motivated violence and intimidation, mainly carried out by ZANU-PF supporters.

The Commonwealth observers also accused the ruling party of using its incumbency to exploit state resources for the benefit of its electoral campaign. They also said thousands of Zimbabweans were denied their right to vote, either by problems with the voter-registration process or because of what they call "an inexplicable reduction in the number of polling stations in urban areas."

South Africa has proposed that Mr. Mugabe and Mr. Tsvangirai join hands in a government of national unity to put an end to the political crisis. But Mr. Tsvangirai has rejected the idea outright, and several ZANU-PF officials have indicated Mr. Mugabe is not interested either.

Some analysts are suggesting new elections, overseen by the United Nations or some other neutral body, might be the only way out of the standoff.