Opposition leader Morgan Tsvangirai has returned to Zimbabwe after an absence of more than two months.
The leader of the Movement for Democratic Change is to have fresh talks with President Robert Mugabe on a stalled power-sharing deal.
The rivals will discuss a four-month-old unity government agreement, which has never been implemented.
Mr Tsvangirai has been away amid a now-resolved dispute over the government's failure to issue him a new passport.
He left Zimbabwe on 10 November for a summit in Johannesburg, where regional leaders tried and failed to push the rivals into a compromise on forming a unity government.
He has spent much of the last two months in Botswana but he flew home via South Africa on Saturday.
Mr Tsvangirai, who remains prime minister-designate, and Mr Mugabe are due to meet on Monday for talks mediated by South African President Kgalema Motlanthe, his predecessor Thabo Mbeki and Mozambican leader Armando Emilio Guebuza.
The MDC leader is expected to meet members of his party's national executive this weekend.
"I'm glad to be back home," Mr Tsvangirai said after arriving in Zimbabwe's capital Harare from Johannesburg. "I hope the meeting will find a lasting solution to the crisis."
However, he said the MDC "will not be bulldozed into an agreement which does not meet the aspirations of the people of Zimbabwe."
Under September's power-sharing agreement, Mr Tsvangirai is to become prime minister while Mr Mugabe remains as president.
Security forces on alert
Security forces have been put on high alert around Zimbabwe's capital in advance of what the government says will be an attempt to overthrow Mr Mugabe.
Tanks have been seen moving into townships around Harare.
The National Constitutional Assembly, representing the country's labour unions, student movements and human rights organisations, has called for mass protests next week to demand that Mr Mugabe abide by an agreement reached last year to form a coalition government.
But the government has said it views such demonstrations as nothing short of a coup attempt that it promises to put down violently.
According to reports on state-controlled television, "security agents have been put on high alert" and all police leave has been cancelled.