Zimbabwean Prime Minister Morgan Tsvangirai has called for a “divorce” from his national unity government colleague President Robert Mugabe.
Mr Tsvangirai organised a news conference after his ally, Energy Minister Elton Mangoma, was arrested.
He said the relationship between the parties had broken down and called for elections to be held.
Former foes Mr Mugabe and Mr Tsvangirai joined in a unity government two years ago after a disputed election.
But Mr Tsvangirai told the news conference: “We have reached a moment where we are saying, let’s agree that this is not working, it’s dysfunctional.
“If people find that a marriage has reached irreconcilable differences, they agree to a divorce.”
He said elections should be held under the auspices of Sadc (Southern African Development Community).
Mr Mangoma, a founder of Mr Tsvangirai’s Movement for Democratic Change (MDC), was taken from his offices by three plain-clothes police on Thursday.
A police spokesman could not confirm whether Mr Mangoma had been arrested or was just being questioned, and no reasons were given for his detention.
Reports say the arrest is believed to be in connection with a fuel deal the minister made in December with a little-known South African company.
MPs from Mr Mugabe’s Zanu-PF party accused Mr Mangoma of bypassing tender procedures and also claimed that only a fraction of the fuel paid for had actually been delivered.
He denies any wrongdoing and says all the fuel was delivered.
The MDC and Zanu-PF agreed to share power after disputes over the 2008 election which saw many thousands of MDC activists forced from their homes by pro-Mugabe militias.
The MDC won a majority of seats in parliament but Mr Tsvangirai pulled out of the presidential run-off, saying he wanted to save his supporters’ lives.