"Our position as of now is that a false settlement is riskier than no settlement," said Nelson Chamisa, spokesperson for the Movement for Democratic Change (MDC).
He said that the party wanted a deal that would give it "the influence to change the situation of the people of Zimbabwe", who face widespread food shortages and inflation.
Party leaders plan to meet on Friday to consider the future of the power-sharing deal signed nearly two months ago, after a summit of the Southern African Development Community (SADC) failed to broker a compromise.
"The purpose of the meeting is to deliberate on the SADC summit and the future of the dialogue process following the outcome of the summit," he said.
"We are getting the entire party leadership to reflect on this to sculpt a way forward," he added.
The summit in Johannesburg on Sunday called for President Robert Mugabe and MDC leader Morgan Tsvangirai to form a unity government immediately, saying the parties should jointly control the disputed home affairs ministry, which runs the police.
Tsvangirai, who defeated Mugabe in March elections, has rejected their proposal as unworkable.
Mugabe said on Monday that Zimbabwe would form a government soon, despite the disagreement. – AFP