Heads of state of the AU, meeting in Egypt, are likely to press Mugabe to enter talks with opposition leader Morgan Tsvangirai to end the political crisis in a country where a hyperinflation-wrecked economy has produced millions of refugees.
U.S. Secretary of State Condoleezza Rice has urged support for international action against Mugabe's government, including U.N.-authorised sanctions and an arms embargo.
But the AU seems reluctant to back calls for sanctions, favouring instead a Kenyan-style power-sharing transition.
In an apparent response to pressure for talks, the 84-year-old Mugabe - who has held power for 28 years - said in an inaugural speech on Sunday he was committed to dialogue with the opposition Movement for Democratic Change (MDC).
Tsvangirai has said the MDC was also committed to AU-sponsored talks, though no negotiations have started. But he said he would ask the AU not to recognise Mugabe's re-election.
The MDC said the AU should not welcome Mugabe at the summit.
"I don't think it would be right for the African Union to welcome him after all he has done," MDC vice president Thokozani Khupe said in Sharm el-Sheikh in Egypt, the summit venue.
"I think it is important that the African leaders break the silence. It is high time they call a spade a spade," said Khupe, adding she had no plans to talk to the Zimbabwean delegation on the sidelines of the summit.
Mugabe left Harare on Sunday night to attend the summit, the state-run Herald newspaper said.
The AU summit may be split between critics of Mugabe, like Kenya, and opponents of any action against him led by South African President Thabo Mbeki, who has been widely criticised for taking a soft line with his neighbour.
NEW MANDATE
Kenya's Prime Minister Raila Odinga was quoted on Sunday as saying the AU should deploy troops.
"What is happening in Zimbabwe is a shame and an embarrassment to Africa in the eyes of the international community and should be denounced," he said.
But AU security chief Ramtane Lamamra played down the prospects of peacekeepers being sent.
Ethiopian Prime Minister Meles Zenawi said it was important the two parties talked, adding it was too soon to talk of foreign peacekeeping forces being sent to Zimbabwe.
"There has to be some sort of negotiations between the parties," he said. "If not, polarisation will be the result."
He added: "There cannot be a sustainable solution to the Zimbabwean crisis under the leadership of one or the other party."
Djibouti Foreign Minister Mahamoud Ali Youssouf said Africa had to help prevent civil war in Zimbabwe.
Mugabe began another five-year term on Sunday after being declared the overwhelming winner of an election which poll monitors said was marked by violence and intimidation.
Mugabe, in power since independence from Britain in 1980, was quickly sworn in to allow him to attend the summit.
Tsvangirai withdrew a week before the election, saying a systematic campaign of violence had made a free and fair ballot impossible. Mugabe won 85.51 percent of the votes, according to the Electoral Commission.
Human rights groups and witnesses accused pro-Mugabe militias of forcing people to vote in some areas.
Regional observers said the ballot did not reflect the will of Zimbabweans, adding that pre-election conditions fell short of Southern African Development Community principles and guidelines for elections.
Pan-African parliament observers said the election was so flawed it should be rerun.
