Zimbabwe's Prime Minister Morgan Tsvangirai has said his MDC party has "disengaged" from the unity government over the treatment of his senior aide.
Senior MDC official Roy Bennett was detained earlier this week and ordered to stand trial on arms and terrorism charges. He was released on bail two days later but Mr Tsvangarai's spokesperson insisted the boycott would continue, the BBC reports.
Mr Tsvangirai said the detention showed Zanu-PF was an "unreliable" partner and 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," the Reuters news agency quotes him as saying.
He said all outstanding issues of a power-sharing deal had to be dealt with before the MDC would work with Zanu-PF.
Mr Mugabe and Mr Tsvangirai agreed to share power in February after disputed elections last year marred by violence.
But since then their parties have failed to agree on appointees for provincial governors, the central bank governor and the attorney general.
The Movement for Democratic Change also accuses Zanu-PF of persecuting its legislators and activists.