There can no longer be any doubt that President Mugabe has no intention of honouring the deal to share power with Morgan Tsvangirai, the leader of the opposition Movement for Democratic Change. His acceptance of the formula negotiated by Thabo Mbeki, South Africa's former President, appeared purely tactical - a way of buying time, alleviating the growing pressure from Zimbabwe's anxious neighbours and throwing a sop to the millions of Zimbabweans outraged at his Government's electoral fraud and intimidation.

Only now, however, has the depth of the wily Mr Mugabe's cynicism and opportunism become clear. He has refused to cede any power to his opponent, insisting on keeping the main ministries for his minority Zanu (PF) party and retaining control of the apparatus of intimidation - the police, army and security agencies - as well as foreign affairs, mining and land. Mr Tsvangirai has been offered only the Finance Ministry, a poisoned chalice that would give him responsibility, without any real leverage, for coping with an inflation rate of some 231 million per cent.

Mr Tsvangirai has rightly decided that this is not power-sharing but a power grab, and has refused to conclude an agreement. Meanwhile, Mr Mbeki arrived in Harare yesterday in a last-ditch attempt to rescue the deal that he mediated a month ago. This time, however, he comes without the authority of his country's presidency behind him. There is little indication that Mr Mugabe will now pay any attention to his views or make any concession to his political rival. The hopes that Zimbabwe might follow the example of Kenya and forge out of electoral antagonism a government of national unity to avert social breakdown now look rashly optimistic.

Mr Tsvangirai is in a difficult position. He has on his side moral authority, an electoral victory and a majority in the first Zimbabwean Parliament not to be dominated by Zanu (PF). All that counts as nothing against the thuggish intimidation, political adroitness and loyalty of the police and bully-boy “veterans” ready to attack any opponent, which Mr Mugabe can still command. The would-be prime minister is not helped by his own lack of political experience and naivety, which the President has exploited to thwart him. Unilaterally, Mr Mugabe has already appointed two members of his party as vice-presidents.

The West also faces a dilemma. Should it encourage Mr Tsvangirai to continue negotiating and offer him the emergency aid essential if Zimbabwe is to escape disaster? The humanitarian arguments are compelling. Aid agencies say that five million people, almost half the population, now face starvation. Many children in rural areas are sick from malnutrition. The Harare Government is indifferent to their fate, and has done almost nothing to relieve the suffering apart from allowing a partial resumption of food aid by foreign agencies. There is no scope for sanctions that might add to the suffering. Zimbabweans should not be punished for Mr Mugabe's actions.

In the longer term, time is on Mr Tsvangirai's side. With Mr Mbeki's resignation, Mr Mugabe has lost his only apologist; Jacob Zuma would certainly take a tougher line. Zimbabwe's neighbours are growing increasingly restless with his intransigence. Unless Mr Mugabe cuts a deal now, he will soon find he is totally isolated. He and his cronies have the most to lose.