Zimbabwe's main opposition party says it has formally pulled out of the presidential run-off election scheduled for Friday.

Movement for Democratic Change spokesman Nelson Chamisa says the party hand-delivered its notice of withdrawal to Zimbabwe's electoral commission Tuesday.

Opposition leader Morgan Tsvangirai announced his withdrawal from the run-off on Sunday, saying violence against his supporters made the election impossible.

However, Zimbabwe's ruling party and electoral officials have indicated the run-off will go ahead as planned.

Today, the Congress of South African Trade Unions (COSATU) called on workers around the world to help isolate Zimbabwe's president, Robert Mugabe, and his government.

In a statement, COSATU expressed sympathy for Tsvangirai's decision to back out of the run-off. It said Mr. Mugabe's ZANU-PF party had made "a declaration of war" against the Zimbabwean people.

On Monday, the U.N. Security Council condemned the violence and intimidation against the opposition in Zimbabwe, saying it is not possible to hold a free and fair presidential run-off.

The 15-member body unanimously adopted the non-binding statement which was the council's first action on the Zimbabwe crisis.

U.N. Secretary-General Ban Ki-moon urged Zimbabwe to postpone Friday's election, saying a vote held in the current conditions would lack all legitimacy.

The MDC says Mugabe supporters have killed more than 80 opposition activists since the first round of voting in March. Zimbabwe's U.N. ambassador Boniface Chidyausiku dismissed the allegations.

Opposition leader Tsvangirai took refuge at the Dutch embassy in Harare Sunday because of fears for his safety. Mr. Tsvangirai says he intends to leave the embassy Wednesday, if it is safe.

Mr. Tsvangirai defeated President Mugabe in elections on March 29. But the official tally. released more than a month later, showed him falling short of the majority needed to avoid a second-round vote.

Some information for this report was provided by AFP and Reuters.