Zimbabwe's Prime Minister Morgan Tsvangirai called on Thursday for a "divorce" in the unity government, proposing elections under a roadmap by the Southern African Development Community.

"We have reached a moment where we are saying, let's agree that this is not working, it's dysfunctional," Tsvangirai told a news conference at his party's headquarters.

"Let's make arrangements to go for elections under a roadmap designed by SADC so that we have a clear, legitimate government."

"Even those with legendary patience, like some of us, have reached a stage where we are saying enough is enough. There is obviously a breakdown in the relationship between the parties," Tsvangirai said.

"If people find that a marriage has reached irreconcilable differences, then agree to a divorce."

Tsvangirai spoke hours after police detained energy minister Elton Mangoma, a key member of his Movement for Democratic Change (MDC), on undisclosed charges.

The MDC suffered another blow Thursday when the Supreme Court nullified the 2008 election of party chairman Lovemore Moyo as speaker of parliament, following an appeal by Mugabe's close ally, Jonathan Moyo.

Tsvangirai said Mangoma's arrest by a police constable was a reflection of Mugabe's ZANU-PF party's "total disregard to the basic tenets of decency."

"His arrest is an assault on the global political agreement," the deal that created the unity government two years ago, Tsvangirai said.