Tsvangirai said his Movement for Democratic Change would disengage from President Robert Mugabe’s "dishonest and unreliable" ZANU-PF party in the country’s unity cabinet set up in February.
"It is our right to disengage from a dishonest and unreliable partner. In this regard, whilst being in government we shall forthwith disengage from ZANU-PF and in particular from cabinet and the council of ministers until such time as confidence and respect are restored amongst us," Tsvangirai told reporters.
The fresh crisis in Zimbabwe comes after a court this week ordered the prison detention of Roy Bennett, a senior MDC official, and ruled that he should stand trial on terrorism charges.
Tsvangirai said the detention of Bennett showed that Mugabe and his ZANU-PF party regarded the MDC as a junior partner and that the power-sharing administration would collapse if the president continued his unilateral rule.
"The … detention of our party treasurer Roy Bennett has brought home the fiction of the credibility and integrity of the transitional government. It has brought home the self-evident fact that ZANU-PF see us as a junior, fickle and unserious movement," Tsvangirai said.
He said if the new constitutional crisis escalated further, it would only be resolved by the holding of fresh elections under supervision of the United Nations and regional body the Southern African Development Community.