I might quit Zimbabwe election, says Mugabe's rival

And as violence continues to rise, Britain, the U.S. and a number of African nations called for calm ahead of Friday's vote.

Morgan Tsvangirai's Movement for Democratic Change says at least 70 of its supporters have been killed since March.

Clinging to power: President Robert Mugabe addressing his supporters today (left), Opposition leader Morgan Tsvangirai is considering pulling out of the presidential run-off election

'There is a huge avalanche of calls and pressure from supporters across the country not to accept to be participants in this charade,' spokesman Nelson Chamisa said.

Earlier this week, three MDC activists and a passer-by were killed by a mob from President Robert Mugabe's ruling Zanu PF party in Chitungwiza, 15 miles south of the capital Harare.

All had their skulls smashed and some had lips and genitals cut off and eyes gouged out.

Yesterday Gordon Brown attacked Mugabe's 'obscene abuse of power'.

He emerged from an EU summit in Brussels to condemn the 'criminal cabal' surrounding the president.

'The eyes of the world are on Zimbabwe' said Mr Brown. 'People should be horrified by what is happening to opposition candidates.'

Mugabe, 84, is fighting to cling on to power in the country he has ruled since independence in 1980.

Yesterday he said he would not leave office until all land was returned to the majority black population.

'I walk on this land. I farm on this land. I sleep on it - that is truly our number one legacy,' he told the Herald newspaper.

Mugabe embarked on a chaotic land reform programme at the turn of the decade which saw some 4,000 white-owned farms expropriated by the state.

Meanwhile, Morgan Tsvangirai's deputy, Tendai Biti, was last night ordered to be held on treason and other charges until after the poll.

He has been in custody for a week and could face a death sentence. A judge ordered him to be detained until July 5.

Charged: Tendai Biti, in red sweater, appears in court in Harare