Harare - Zimbabwe's opposition on Tuesday hand-delivered a letter to the country's electoral commission confirming that its leader Morgan Tsvangirai will not participate in this week's presidential run-off, a party spokesperson said.

"They are now happy recipients of that letter from the MDC," Movement for Democratic Change (MDC) spokesperson Nelson Chamisa said.

"In the letter we are stating clearly that we are not participating in this election."

He added: "We are saying a free and fair election is impossible in the prevailing circumstances."

The letter adds that if Zimbabwe's ruling Zanu-PF party goes ahead with the vote set for Friday, "it has no endorsement of the MDC and indeed the majority of the people of Zimbabwe."

According to Chamisa, "the election result of March 29 should stand until a free and fair election is held."

Tsvangirai defeated President Robert Mugabe in the March 29 first round of the election, but with an official vote total just short of an outright majority.

Mugabe's ruling party also lost its parliamentary majority in the election for the first time since independence from Britain in 1980.

Tsvangirai announced on Sunday he was withdrawing from the run-off poll since violence had made a fair election impossible.

However, Zimbabwe's ruling party and electoral officials have said they were pushing ahead with Friday's run-off because Tsvangirai had not formally confirmed his withdrawal.

The opposition claims more than 80 of its supporters have been killed in a campaign of intimidation ahead of the vote, and Tsvangirai has been holed up in the Dutch embassy in Harare for nearly two days, saying he will remain there until he feels safe.

International calls have intensified for the government to postpone the run-off election. - Sapa-AFP