Robert Mugabe's aides have told Zimbabwe's opposition leaders that he is prepared to give up power in return for guarantees, including immunity from prosecution for past crimes.

But the aides have warned that if the Movement for Democratic Change does not agree then Mugabe is threatening to declare emergency rule and force another presidential election in 90 days, according to senior opposition sources.

The opposition said the MDC leadership is in direct talks with the highest levels of the army but it is treating the approach with caution because they are distrustful of the individuals involved and calling for direct contact with the president, fearing delaying tactics.

Those fears were reinforced last night when at one point Zimbabwe's election commission abruptly halted the release of official results from the Saturday's election for "logistical reasons" and the police raided opposition offices.

The MDC's presidential candidate, Morgan Tsvangirai, has already claimed victory on the basis of his party's tally of the count at polling stations.

The police arrested at least two foreign journalists, one from Britain and a New York Times correspondent, who are banned from Zimbabwe under draconian media laws.

A senior MDC source said "the ball is rolling" in persuading Mugabe to recognise defeat in the presidential election after negotiations with the security establishment and contacts with high levels of Zanu-PF.

The source said the party was approached by senior Zanu-PF officials who said they were speaking for Mugabe and that he is prepared to resign if there are guarantees that he and senior aides would not be prosecuted.

He said there were other demands which he did not specify but the approach was being treated with caution because officials who negotiated for Mugabe in the past had offered commitments which the president had not fulfilled. The MDC wants to talk to Mugabe directly.

Another MDC official said the party is maintaining a tough negotiating stance in contacts with other elements of the ruling party and had refused a Zanu-PF demand for up to four seats in the cabinet.

He said the MDC had rejected power sharing offers because it had won the presidential race outright even though the electoral commission has yet to start releasing results.

"We cannot share power when we've won. If you've won the cup you don't share it," the opposition official said.

But senior Zanu-PF officials are attempting to pressure the opposition with the threat of a run-off presidential election by ensuring Tsvangirai's proportion of the vote falls below 50% and then delaying the second round. It should be held within 21 days but the ruling party is threatening to postpone it for three months during which Mugabe's term in office would expire and he would extend his rule by emergency decree.

The MDC's leadership has also opened direct talks with the "top, top" of the army according to the source.

The source said that the military leadership is looking for "guarantees for their conditions of service" and to keep farms confiscated from whites provided they are productive. The MDC said it has no problems with those issues.

Another MDC source said the party had assured Zanu-PF and security officials they would not be prosecuted for past crimes.

The opposition believes the approaches mark a recognition by Mugabe that support for him within Zanu-PF has eroded since the election. Now, important elements of Mugabe's party are willing to do a deal because they realise the election results could not be manipulated to overturn a clear opposition victory and that there is little hope of winning a second round of presidential elections without resorting to violence or fraud.

Mugabe's position was further undermined on Wednesday when Zanu-PF lost control of parliament for the first time since independence in 1980.

Publicly Zanu-PF has vowed to "fight on" and the opposition said it was still preparing for a second round of elections if Mugabe did not bow to pressure to go.

Bright Matonga, Zanu-PF's deputy information minister, took a defiant position, saying that the party had "let the president down" by not winning Saturday's election.

"Zanu-PF is ready for a run-off, we are ready for a resulting victory," he said.

"In terms of strategy, we only applied 25% of our energy into this campaign ... (The run-off) is when we are going to unleash the other 75% that we did not apply in the first case."

The MDC fears that what will be unleashed is an extremely violent campaign because that is its last hope Zanu-PF has of curbing support for the opposition.