Zimbabwean parties are to meet again next week after power-sharing talks ended without a deal last night.
An official said regional leaders would discuss the stalemate between President Robert Mugabe and his rivals at a summit in Botswana or South Africa next week that all Zimbabwean leaders have agreed to attend.
"For us as the MDC, this is probably the darkest day of our lives," opposition leader Morgan Tsvangirai said after a 12-hour meeting in Harare, which was billed as a last-ditch effort to save the pact.
A unity government is seen as the best chance of preventing total collapse in once-prosperous Zimbabwe, where prices double every day, and more than 2,000 people have died in a cholera epidemic.
But a September power-sharing agreement has stalled amid fighting over who should control key ministries and regional leaders have failed to secure a compromise, despite international calls for stronger action.
Mr Mugabe said talks had broken down but would continue, and blamed Mr Tsvangirai's opposition Movement for Democratic Change for blocking proposals put forward by the Southern African Development Community (SADC) at the meeting.
Mr Tsvangirai reiterated that the MDC was committed to the deal but only if Mr Mugabe cedes control of powerful ministries, such as home affairs, finance and information.
South African President Kgalema Motlanthe, Mozambique leader Armando Guebuza and Thabo Mbeki, regional mediator and South Africa's former president, attended the Harare meeting.
SADC executive secretary Tomaz Salomao said next Monday's emergency summit would discuss Tsvangirai's demands.
Earlier, the MDC said abductions of its members, which it blames on Mr Mugabe's Zanu-PF, proved "beyond a shadow of a doubt" its rivals had not respected the spirit of the September pact.
Mr Tsvangirai won a presidential election last March but by too few votes for an outright victory. He pulled out of the subsequent run-off, citing violence against MDC supporters.
Zimbabwe's parliament is due to resume sitting on Tuesday.
Reuters