The United States criticised Africa for lack of action on Zimbabwe on Thursday and South Africa expressed concern for the first time over a long delay in issuing results from a March 29 presidential election.

As U.S. President George W. Bush called for more vigorous action, opposition leader Morgan Tsvangirai said South African President Thabo Mbeki must stand down as a mediator and make way for a new initiative.

"More leaders in the region need to speak out and the United Nations and the A.U. (African Union) must play an active role in resolving the situation in Zimbabwe," Bush told reporters after meeting British Prime Minister Gordon Brown in Washington.

His remarks echoed a tough statement from U.S. Secretary of State Condoleezza Rice who asked at a news conference: "Where is the concern from the African Union and from Zimbabwe's neighbours about what is going on in Zimbabwe?"

African reaction has been subdued to events in Zimbabwe, where a 19-day delay in issuing results of the presidential poll has fuelled fears of violence, although regional leaders called last weekend for the outcome to be announced quickly.

The continent has largely taken its cue from Mbeki, who has been under pressure for insisting on a softly softly diplomatic approach to President Robert Mugabe, despite the collapse of Zimbabwe's economy.

In power since independence from Britain in 1980, Mugabe is preparing to contest a second ballot run-off against Tsvangirai, leader of the Movement for Democratic Change, even though the results of the first round of voting have not been issued.

Mugabe, 84, is due on Friday to address a crowd in a Harare township to mark the 28th anniversary of the nation's independence. It will be his first major speech since the elections and he may use it to attack Western powers.

The leader has accused the MDC of being a puppet of Britain. He said on Thursday imperialist forces were infiltrating Zimbabwe and it was in danger of being re-colonised.

"As long as I am still on this earth, as long as I am still breathing, the country shall never be a colony again. Never shall this country be a British colony again," Mugabe said at a sports centre in Harare, according to the online version of the government-run Herald newspaper.

PRESSURE ON SADC

Tsvangirai, who has declared himself and his party the winners of the elections, told BBC television news in an interview that members of Mugabe's ruling ZANU-PF had negotiated for a government of national unity days after the elections.

Tsvangirai said part of the deal had been that no one should lose their jobs or face prosecution. The immunity deal would include Mugabe, he added.

But hardliners put paid to it, he said.

"The very same people who were coming to us for discussions organised the meeting and did not turn up for almost two hours, our guys left and we realised that the situation had totally changed, they were back to their plan," he said.

Earlier he said he had asked Zambian President Levy Mwanawasa, chairman of the Southern African Development Community (SADC), to launch a new initiative.

"President Mbeki needs to be relieved from his duty," Tsvangirai told a news conference in Johannesburg, adding that Mugabe had "unleashed an orgy of violence against the people" after the election.

Mbeki led a failed SADC mediation last year.

The MDC said hundreds of supporters had been seriously injured in attacks by ZANU-PF. The opposition says Mugabe is using militias to intimidate opposition supporters and help him rig victory in an expected run-off election against Tsvangirai.

Tsvangirai suggested there may need to be a special United Nations tribunal to judge crimes committed in Zimbabwe.

"I think the current wave of violence against the people must stop and the only way to stop (it) is that those who are committing those crimes must know that they must be answerable one day," he said.

POLICY SHIFT

In a policy shift, Mbeki's government called for the results to be issued rapidly and said it was concerned by the delay.

"When elections are held and results are not released two weeks after, it is obviously of great concern," government spokesman Themba Maseko said in Cape Town.

Mbeki had previously said the electoral process must take its course and there was no crisis after the elections.

His stance was seen as backing Mugabe over the delay.

Although ZANU-PF lost control of parliament for the first time, no results have been released from a presidential poll.

"The Zimbabweans need to be informed about those reasons for holding the results. But the most important thing is that the results need to be verified and released as soon as possible," Maseko said, briefing reporters on a Wednesday cabinet meeting.