British Foreign Secretary David Miliband on Sunday called on the international community to unite in condemning the re-election of Zimbabwean President Robert Mugabe and said the opposition should now come to power.

Miliband, who is in South Africa for talks with the government, visited a church in Johannesburg that houses thousands of refugees from neighbouring Zimbabwe, and said the world had to act together to end their hardships.

"No one who meets the people here could do anything other than redouble their efforts to secure international consensus that the Mugabe regime is not a legitimate representation of the will of the people of Zimbabwe," Miliband said on Radio 702.

"It is imperative that a government be formed with respect to the 29th of March result because this is now a crisis and it's affecting the whole of southern Africa," Miliband said.

Morgan Tsvangirai, the leader of the opposition Movement for Democratic Change, beat Mugabe in the March presidential election, but not by enough votes to avoid a run-off. Mugabe won the second round vote late last month after Tsvangirai pulled out citing state-sponsored violence against his supporters.

Mugabe, who has ruled Zimbabwe for 28 years, has been defiant in the face of growing condemnation from Western governments and some African neighbours. President Thabo Mbeki of regional powerhouse South Africa has been criticised at home and abroad for his quiet diplomacy approach to the crisis.

Mbeki, acting as regional mediator, met Mugabe on Saturday to try to help end the turmoil. Tsvangirai, who has accused Mbeki of siding with Mugabe, declined to meet with him.

Britain said last week it was preparing tougher sanctions against specific members of the Zimbabwean government.

South African foreign affairs spokesman Ronnie Mamoepa said in a statement Miliband would meet with his South African counterpart Nkosazana Dlamini-Zuma and other senior government officials from Monday, and Zimbabwe would be on the agenda.

Miliband will not meet with Mbeki, who will be attending a summit of the Group of Eight rich nations in Japan.