Mugabe likely to be inaugurated on Sunday-sources

* Mugabe heading for landslide-government sources

* AU officials wary of sanctions

* U.N. Security Council "deeply regrets" election

HARARE, June 28 (Reuters) - Zimbabwe's President Robert Mugabe is heading for a landslide victory in a one-candidate election boycotted by the opposition and is expected to be sworn in on Sunday, government sources said.

The sources told Reuters official tallies from two-thirds of polling stations showed Mugabe, 84, defeating opposition leader Morgan Tsvangirai by a huge margin in a poll critics have condemned as a sham.

Tsvangirai's name remained on ballot papers after electoral authorities refused to accept his decision to withdraw a week ago on the grounds of violence against his supporters. He has taken refuge in the Dutch embassy since then.

"The tallies are indicating that despite the wishes of our detractors and the propaganda of our enemies, the voter turnout was very big and that we are going to see a landslide victory," said one of the officials, who declined to be identified.

Witnesses and monitors reported a low turnout in many areas in Friday's election, which was widely condemned after Tsvangirai withdrew, saying almost 90 of his supporters had been killed in systematic violence by Mugabe's supporters.

They said voters in some areas had been forced to vote for the president, who has held uninterrupted power for 28 years.

Tsvangirai said millions of people stayed away from polling stations despite systematic intimidation.

The opposition leader and his Movement for Democratic Change (MDC) won presidential and parliamentary elections on March 29 but Tsvangirai fell short of the majority needed for outright victory.

The decision to go ahead with the poll brought unprecedented condemnation of Mugabe from inside and outside Africa and the vote was widely dismissed as illegitimate.

The U.N. Security Council unanimously expressed deep regret and said a free and fair vote had been impossible.

Many Western leaders urged the African Union to take action at a summit in Egypt on Monday, saying the political turmoil and economic meltdown in Zimbabwe threatened regional security.

The MDC said it would lobby the summit leaders.

"The summit has to take a firm position on the transition we seek. It's now a matter of peace and security. We hope the matter gets the urgent attention it deserves. We should not wait for rivers of blood and the complete breakdown of order," MDC spokesman Nelson Chamisa said.

Senior officials attending a preparatory summit meeting shied away from Western proposals for stronger international sanctions against Mugabe, saying they were unlikely to work and a power-sharing deal should be encouraged. (Additional reporting by Nelson Banya and MacDonald Dzirutwe in Harare, Marius Bosch in Johannesburg, Daniel Wallis and Cynthia Johnston in Sharm el Sheikh; Writing by Barry Moody; Editing by Andrew Dobbie)