US President George W. Bush called on Tuesday for an end to Robert Mugabe's "tyranny" in Zimbabwe and urged African leaders who have not yet done so to "join the growing chorus" pushing for his ouster.

"As my administration has made clear, it is time for Robert Mugabe to go," the US president, who hands the keys to the White House to successor Barack Obama on 20 January, said in a statement.

A day after European nations tightened their sanctions on Mugabe and his inner circle, Bush praised African leaders who have been "bravely speaking out" to call for the 84-year-old to step down after 28 years in power.

"We urge others from the region to step up and join the growing chorus of voices calling for an end to Mugabe's tyranny," said the US president.

Former colonial power Britain has led the international calls for Mugabe to resign, with the country's economy in shambles amid a political deadlock after controversial elections earlier this year.

Most of Zimbabwe's neighbours have remained silent or backed floundering negotiations aimed at forming a unity government.

"The United States will continue to work with our partners around the world to halt the violence and stem the humanitarian disaster that the Mugabe regime is inflicting on its people," Bush promised.

"We stand ready to help rebuild Zimbabwe once a legitimate government has been formed that reflects the results of the March elections," said Bush.

South Africa's ruling party boss Jacob Zuma and Namibian President Hifikepunye Pohamba said on Tuesday that they still backed the regional effort to mediate a power-sharing deal in Zimbabwe.

Former South African president Thabo Mbeki brokered an agreement for Mugabe to form a unity government with the opposition in September, but the deal has faltered over disputes about how to divide control of powerful ministries.

Among Zimbabwe's neighbors, only Botswana has taken a tough line against Mugabe — even suggesting that the region cut off fuel shipments to Zimbabwe to force him from power.

AFP