An election runoff between Zimbabwe's President Robert Mugabe and opposition leader Morgan Tsvangirai runoff will be held June 27, the electoral commission said in an announcement published Friday.

The commission had extended the deadline for holding the runoff to 90 days — beyond the legally required 21 days.

Tsvangirai said setting the vote date for June 27 was illegal, but "we will contest."

"This is a regime which operates not on the basis of the law, but operates on the basis of impunity from the law. So they are changing goal posts to suit themselves," he told reporters in Belfast, Northern Ireland, where he was attending an international conference of liberal party members.

The opposition had wanted a May 23 runoff, and said the decision to extend the deadline was "irresponsible."

Tsvangirai claims he won the March 29 presidential race outright. But official results released May 2 show he did not win enough votes to avoid a second round against Mugabe.

Zimbabwe's electoral commission announced the runoff date in the government gazette, saying: "It is hereby notified that the Zimbabwe electoral commission with the approval of the minister of justice made the following notice: a poll shall be taken on Friday, June 27, 2008, for the purpose of electing a person to the office of president."

The Zimbabwe Electoral Commission chairman said in an interview with the Herald newspaper, a government mouthpiece, published Friday that the commission needed "substantial" resources.

"The runoff is a full election and just as big as any general election," the paper quoted George Chiweshe as saying. "Some of the resources were depleted during the first election, so we need more time to prepare for the runoff."

The opposition as well as local and international human rights groups have accused Mugabe's party of using delays to mount a campaign of violence and intimidation against opposition supporters.

Tsvangirai's Movement for Democratic Change said Thursday the postelection violence was intensifying, and that 33 of its supporters and activists had already been killed.

"This country cannot afford 90 days" of more violence and economic instability, the party's secretary-general, Tendai Biti, told reporters Thursday in Johannesburg, South Africa.

Biti and Tsvangirai have been out of the country since shortly after the March 29 vote.

He indicated Tsvangirai would be back in Zimbabwe for a planned campaign rally this weekend, as well as a caucus of members elected to parliament. He said he would return some time after Tsvangirai.

Tsvangirai's party won control of parliament in legislative elections held alongside the presidential vote. It was the first time since independence that Mugabe's party lost control of parliament.