Zimbabwe must guarantee the safety of opposition leader Morgan Tsvangirai as one of several conditions to ensure a fair presidential run-off election, a senior US official said on Monday.

"Right now the conditions aren't there for a free and fair run-off. Certainly we hope the conditions can be put in place," said Jendayi Frazer, the US assistant secretary of state for African affairs.

Those conditions include an end to the violence, which she said is "essentially state-sponsored violence against the opposition" and the deployment of a "massive" number of monitors to visit rural areas.

The authorities would also need to allow in international media as well as provide "some type of security and guarantees for Morgan Tsvangirai's safety," Frazer told reporters.

The head of the Movement for Democratic Change, Morgan Tsvangirai, said he would return home to face incumbent Robert Mugabe in a presidential runoff poll despite the risk of "more violence, more gloom, more betrayal."

The former trade union leader, who beat veteran incumbent Mugabe in a first round of voting in March, set international peacekeepers, election monitors and an end to violence in the country as conditions for the ballot.

The White House on Saturday called for election and UN human rights monitors in Zimbabwe to ensure an end to violence against opposition leaders and their supporters in a presidential run-off.

AFP