Nigeria on Friday rejected the re-election of Zimbabwe's President Robert Mugabe, saying a run-off vote had changed nothing in the country, but stopped short of refusing to recognise his government.

Foreign Minister Ojo Maduekwe said Mugabe should not use the outcome of a June 27 run-off vote, boycotted by opposition leader Morgan Tsvangirai, as a basis for negotiation.

"We express our strong displeasure at the process leading to the election and its outcome ... we therefore do not consider the outcome of that election as a basis for moving forward," Maduekwe told reporters.

"Since the run-off election did not change anything in Zimbabwe we believe that discussions should proceed without any reference to the run-off election," he said in Abuja, capital of Africa's most populous nation.

An African Union summit this week handed Mugabe an unprecedented rebuff, telling him to negotiate a national unity government with Tsvangirai's MDC opposition.

Mugabe said on Friday the opposition must drop its claim to power and accept that he was the rightful head of state.

"We would not like to make any provocative statements by categorically saying whether the Nigerian government recognises the present government or not," Maduekwe said.

"We are looking for a diplomatic solution so that the parties involved will go back to the negotiating table."

Mugabe's supporters have questioned the right of other African countries to criticise Zimbabwe's election.

Nigerian elections in 2007 were so marred by vote rigging and intimidation that foreign observers said they were "not credible".