"Lets go to SADC… We said this issue should be finalised there. This time we won’t fail," he told supporters at a rally.
The power-sharing deal, mediated by former South African president Thabo Mbeki, is seen as Zimbabwe’s best hope for rescuing an economy where fuel and food are scarce and inflation stands at 231 million percent, the world’s highest.
Tsvangirai threatened to pull out of talks a week ago after Mugabe allocated powerful ministries such as defence, finance and home affairs to his own party.
"The sooner we put finality to this stupid debate about the allocation of power the better," Tsvangirai told supporters at the rally in Masvingo, 300 km (186 miles) southeast of Harare.
ZANU-PF’s chief negotiator in the talks, Patrick Chinamasa, played down that issue and reiterated that the party would not bow to any pressure from the SADC, which has become increasingly frustrated by Zimbabwe’s political turmoil.
"They cant impose anything on us, especially on such a small thing as the allocation of ministries," he told the state-run Sunday Mail newspaper.
Zimbabwean President Robert Mugabe, Tsvangirai and Arthur Mutambara, head of the smaller MDC faction, will join the three-way meeting of the heads of state of Angola, Mozambique and Swaziland.
President Kgalema Motlanthe of economic powerhouse South Africa, the current chair of SADC, will lead a delegation to Swaziland, the Foreign Ministry said. Mbeki is expected to brief the meeting on efforts to form a new government in Zimbabwe, it added in a statement.
Mbeki said on Friday a deal was still possible despite another round of inconclusive talks. However, his effectiveness has been thrown into doubt since South Africa’s ruling ANC party forced him to resign.
The MDC has accused him of favouring Mugabe, an issue that Chamisa raised again.
"I suppose that Mbeki seems to be more inclined to appreciate the circumstances from the ZANU-PF point of view than from the MDC point of view," Chamisa told South Africa’s SAfm radio.
"That is the situation and we are hoping that when we go to the troika our side is going to be heard," he added.
Tsvangirai beat Mugabe in a March 29 presidential election but with too few votes to avoid a June run-off, which was won by Mugabe unopposed after Tsvangirai pulled out, citing violence and intimidation against his supporters.
Mugabe’s victory in the run-off was condemned around the world and prompted tougher sanctions from Western countries whose support is vital to revive Zimbabwe’s ruined economy.