Gordon Brown urged African leaders to unite in condemning Robert Mugabe, promising the world would pump money into Zimbabwe if democracy there was restored.
As Mr Mugabe sealed victory in the run-off election, despite observers declaring the one-man election as neither free nor fair, Africa Union leaders gathered for a summit in Egypt.
The Prime Minister said he hoped they would send UN-backed envoys to find a way forward, amid reports Mr Mugabe had agreed to talks with the opposition.
He told CNN: "I think what we are now looking for is that combination of African countries in the African Union, working I hope with the United Nations, sending envoys to Zimbabwe to see what progress can be made, to see what the way forward is.
"And let me also say that we and a group of countries are working together and prepared to contribute substantially financially to the reconstruction of Zimbabwe.
"Countries round the world will do so as long as it is restored as a democracy."
Foreign Office Minister Lord Malloch-Brown, who is attending the AU gathering, earlier told the BBC that Zimbabwe's neighbours should "do whatever it takes" to get rid of Mr Mugabe.
And Archbishop Desmond Tutu said there was a "very good argument" for the international community considering the use of force to intervene in the country.
His appeal came as African observers in Zimbabwe said the election was not free and fair and supporters of Mugabe were beating people who couldn't prove they voted.
Mr Mugabe was the only candidate in the presidential run-off after Movement for Democratic Change (MDC) leader Morgan Tsvangirai pulled out last week in protest at a brutal Government-organised campaign against his supporters.
