Johannesburg, South Africa — President Mugabe announced yesterday that he would form a new government without the opposition, placing the future of Zimbabwe’s power-sharing talks in grave doubt.

The main goal of the talks, mediated by President Mbeki of South Africa, was to bring Mr. Mugabe and his opponents together in an administration.

But the leader of the Movement for Democratic Change, Morgan Tsvangirai, refused to join any government that allowed Mr. Mugabe to keep his executive powers.

One day after the opposition’s newly elected members of Parliament heckled him during parliament’s official opening, Mr Mugabe said he would choose a cabinet without them.

“We shall soon be setting up a government. The MDC does not want to come in apparently,” he said.

In a speech reported in the state newspaper, the Herald, Mr. Mugabe claimed that Britain had given new promises to the MDC.

“This time they have been promised by the British that sanctions would be more devastating, that in six months’ time the government will collapse. I do not know when that day will come. I wish Tsvangirai well on that day,” he said.

But Mr. Mugabe’s Zanu-PF party is deeply split and the president signalled that a ministerial purge was imminent. “This cabinet that I had was the worst in history,” he said, conveniently ignoring the fact that he appointed them and presided over their actions. “They look at themselves. They are unreliable, but not all of them.”

Mr. Mugabe appears to be positioning the cabinet minister who is closest to the powerful military leadership, Emmerson Mnangagwa, as his favored successor. Nelson Chamisa, the MDC’s spokesman, said: “It’s very clear that if he announces the new cabinet it’s a declaration of war against the people. You can’t just have a cabinet without a mandate. Otherwise what he is doing is a recipe for disaster.”