Kenyan Prime Minister Raila Odinga has urged the African Union to suspend Zimbabwe's Robert Mugabe until he allows free and fair elections.
His appeal at an African Union summit in Egypt came as Zimbabwe's opposition said the country faced a constitutional crisis after an "illegal" poll.
Mr Mugabe claimed victory as the sole candidate in the presidential re-run after the opposition leader withdrew.
Meanwhile, Italy recalled its envoy to Zimbabwe in protest at the situation.
The move followed a call by Italy's foreign minister last week for European Union nations to begin withdrawing their ambassadors to Harare.
In a statement on Monday, the Italian foreign ministry said pulling out all EU ambassadors would signal the "firmness and disapproval that is shared by the international community" at the conduct of the run-off.
African observers said the election had been undermined by pre-poll violence.
The situation in Zimbabwe overshadowed the African Union summit in Egypt.
I would expect them to have very, very strong words for [Mr Mugabe]
Jendayi Frazer US Assistant Secretary of State for Africa
The opposition is prepared to take part in a transitional arrangement or a government of national unity, but it says there are no negotiations currently under way between Mr Tsvangirai and the ruling Zanu-PF party.
The MDC is asking the AU to appoint three eminent African envoys to work full time on the crisis.
The US ambassador to the United Nations, Zalmay Khalilzad, says he is pressing for the Security Council to impose sanctions against Zimbabwe.
The US is expected to present a draft resolution on Wednesday calling for an arms embargo and a freeze on the assets of key individuals and companies.
Correspondents say it may be difficult to persuade South Africa, Russia, China and others to accept UN sanctions.
White House spokeswoman Dana Perino has suggested the US may impose unilateral diplomatic and economic sanctions.
Few African leaders have spoken out about the election result while AU discussions continue.
The South African presidency said it would consider reports from election observers together with other members of the Southern African Development Community (Sadc) before adopting a unified position regarding the result.
President Jakaya Kikwete of Tanzania, the African Union chairman, pointedly congratulated the people of Zimbabwe over the election, but not Mr Mugabe himself.
Africa's longest serving leader, Gabon President Omar Bongo, has given the strongest suggestion of recognising Mr Mugabe as president, saying "he was elected, he took an oath, and he is here with us, so he is president".
US Assistant Secretary of State for Africa Jendayi Frazer said she expected African leaders to take a harder line with Mr Mugabe behind closed doors.
"I would suggest not to take the soft words of the opening plenary as a reflection of the deep concern of the leaders here for the situation in Zimbabwe," she said.
"I would expect them to have very, very strong words for him."
The BBC's southern Africa correspondent Peter Biles says that apart from the recent political violence in Zimbabwe, there is continuing economic hardship, with inflation in the region of nine million per cent and the country heading for the worst harvest in 60 years.
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