HARARE (Reuters) - South Africa's ruling ANC leader Jacob Zuma said he did not expect a free presidential election run-off in Zimbabwe ahead of a meeting on Wednesday between President Thabo Mbeki and Zimbabwe's Robert Mugabe.

Zuma, who has taken a much tougher line on Zimbabwe than Mbeki, used his bluntest language to date on the election.

"I think we'll be lucky if we have a free election," Zuma told Reuters. When asked if he thought the vote would be fair, Zuma replied "I don't think so."

In London, British Prime Minister Gordon Brown said Zuma had told him he supported the deployment of 1,000 ANC monitors to observe the June 27 run-off election.

Mugabe faces opposition challenger Morgan Tsvangirai in the vote next week and the veteran president's supporters have been accused by the opposition, Western countries and human rights groups of a campaign of violence. Mugabe blames his opponents.

Mbeki has led regional mediation efforts in Zimbabwe and has drawn criticism for a diplomatic approach that has failed to end the crisis in the once prosperous country, where economic ruin has driven millions of people into neighbouring states.

The South African president arrived for a meeting with Mugabe at the Zimbabwean ruler's official residence in Zimbabwe's second biggest city, Bulawayo, shortly before 1700 GMT on Wednesday, a Reuters photographer said.

South Africa's Department of Foreign Affairs said the meeting would be a continuation of Mbeki's mediation under a mandate from regional bloc SADC. Zimbabwe's state-owned Herald newspaper said they would discuss the election and campaigns.

Mbeki earlier met Tsvangirai in Harare, the opposition Movement for Democratic Change said.

"(Party) President Tsvangirai met with President Thabo Mbeki in the latter's role as a visiting head of state," the opposition party said.

South Africa's Department of Foreign Affairs said in a statement the meeting between Mbeki and Mugabe would be a continuation of his mediation under a mandate from regional bloc SADC. Zimbabwe's state-owned Herald newspaper said they would discuss the election and campaigns.

Zuma, who defeated Mbeki for the African National Congress leadership last December, has been much more outspoken than the president.

Mugabe, 84, has ruled since independence from Britain in 1980. His support has waned amid a desperate economic crisis that has brought hyperinflation and food shortages.

Food shortages

U.N. food agencies said on Wednesday that more than 5 million people in Zimbabwe risk going hungry by early next year as production of the staple maize in 2008 would be almost 30 percent lower than last year.

The food agency report released [see here PDF] on Wednesday urged the government of Zimbabwe and international community to ensure emergency aid to farms to tackle chronic shortages expected by next January.

Movement for Democratic Change (MDC) leader Tsvangirai won a first round of voting in March, but without enough votes to secure an outright victory, official results showed.

The MDC leader has been repeatedly detained and released during the election campaign and one of his top lieutenants has been arrested and faces a treason charge.

Former U.N. Secretary-General Kofi Annan, writing in Britain's Financial Times, said Zimbabwe needed not only a fair election but reconciliation between its political leaders.

"...there is no doubt that what we are seeing in Zimbabwe is tarnishing the reputation of Africa as a whole in the eyes of both friends and critics," Annan said.

"If the government...cannot ensure a fair vote, Africa must hold it accountable.

"The victor of an unfair vote must be under no illusions: he will neither have the legitimacy to govern, nor receive the support of the international community," Annan said.

Britain and the United States urged Mugabe this week to allow a broader international observer mission. The biggest group is from SADC. Monitors from countries critical of Mugabe have been banned from observing the election.

British Prime Minister Brown told parliament he had spoken on Sunday to Zuma, "and he supported the idea that there would be 1,000 monitors from the ANC party offered to Zimbabwe so that they too can play a part in the election."