Last week the MDC leader threatened to pull out of talks with rival Robert Mugabe, Zimbabwe's president, who allocated powerful ministries such as defence, finance and home affairs to his ruling Zanu-PF party.
After four days of negotiations, Tsvangirai on Saturday described the talks as "a dialogue of the deaf", adding: "It was one-man monologue. Mugabe does not negotiate. He just says 'no'. He was saying 'no' since Monday."
Mugabe had earlier declined to explain the deadlock in the talks, saying only that they "went well in the wrong direction".
The rival parties signed a deal one month ago for Mugabe to remain president and Tsvangirai to assume the new position of prime minister, but they have been unable to reach an agreement on who should control the key cabinet portfolios.
The cabinet posts were supposed to be shared out between their parties and a breakaway faction of the MDC led by Arthur Mutambara.
The parties are expected to join the regional meeting in Swaziland on Monday.
The power-sharing deal, mediated by Thabo Mbeki, the former South African president, may be Zimbabwe's best hope for rescuing an economy where fuel and food are scarce and inflation stands at 231 million per cent.
Patrick Chinamasa, the chief negotiator for Zanu-PF, was quoted in a state-run newspaper on Sunday as saying that the party will not bow to any pressure from the SADC.
He had also told the Herald newspaper that his party agreed to give MDC control of the finance ministry while keeping for itself the key home affairs ministry which oversees the police force.