Zimbabwe's presidential showdown set for June 27

In Belfast, Tsvangirai said he "must return to Zimbabwe to be with our people and to lift them out of the darkness" -but he did not give a date. His spokesman, George Sibotshiwe, said no date had been set.

Tsvangirai has survived three assassination attempts, including one in 1997 by unidentified assailants who tried to throw him out a 10th floor office window. Last year, he was hospitalized after a brutal assault by police at a prayer rally, and images seen around the world of his bruised and swollen face have come to symbolize the challenge dissenters face in Zimbabwe.

But he said he did not fear assassination upon his return, adding that he will face the same risks confronting his rank-and-file supporters.

Human rights groups say dozens of opposition supporters have been killed and hundreds tortured in recent weeks by Zimbabwean security forces and activists loyal to Mugabe. Tens of thousands of opposition supporters also have been driven from their homes, the groups say.

Tsvangirai described Mugabe's government as "a regime which operates not on the basis of the law, but operates on the basis of impunity from the law." He said the June election date was an example of Mugabe officials "changing goal posts to suit themselves."

Zimbabwe law says a runoff should be within 21 days of official election results, which would have been May 23, but the ruling party says the law allows that period to be extended 90 days. The election commission said it set a late June date because it needs to devote "substantial" resources to organizing the runoff.

Tsvangirai said he hoped to persuade new political factions, and even ruling party supporters, to join his Movement for Democratic Change before the runoff.

"We are actually going to broaden the coalition beyond just the MDC, and I am confident that even some members of ZANU-PF would rather work for the MDC than work for Mugabe -who is 84 years by the way," Tsvangirai said.

He said Mugabe's regime hoped to intimidate tens of thousands of voters into staying away from the polls and called on the 15-nation Southern African Development Community to send poll observers to ensure this did not happen.

"Violence has to cease for an election to be conducted. Otherwise that election will not be legitimate," he said.