By Caroline Drees

JOHANNESBURG, May 13 (Reuters) - The leader of Zimbabwe's main opposition group said on Tuesday he would contest a presidential run-off against veteran President Robert Mugabe even if only regional observers could be present.

Movement for Democratic Change (MDC) leader Morgan Tsvangirai had previously called for unfettered access for international observers, which the government rejected. The MDC accuses Mugabe of trying to intimidate voters and rig the poll.

"At the moment the obligation is on (regional group) SADC. I am sure that they will fulfil their obligations, especially to send SADC peacekeepers and observers," Tsvangirai told Reuters in a telephone interview. "For us that is sufficient."

After weeks of equivocation, Tsvangirai said at the weekend he would participate in the run-off to the disputed March 29 polls, but only if international monitors would be present. He also called on the Southern African Development Community to send peacekeepers to instil public confidence in the vote.

The MDC leader travelled to Angola on Saturday to ask President Jose Eduardo dos Santos, who heads SADC's security committee, to push for the peacekeepers. The regional grouping has not said whether it would agree to the request.

Zimbabwe's government rejected any pre-conditions for the run-off, but allowed SADC to monitor the election's first round.

The top U.S. diplomat on Africa on Monday pressed Zimbabwe to allow in large numbers of Western election monitors for the second round.

Asked how long he was willing to wait for a run-off, after electoral authorities said there would likely be a delay, Tsvangirai said any timeframe would have to be "reasonable". By law, the second round should be held within 21 days of the result, announced on May 2, but the period can be extended.

"The thing is that the Zimbabwe Electoral Commission, if it has to extend the time of a run-off, it has to do so within a reasonable period. I'm sure that SADC will also be pressurising them to set a date."

RETURN HOME

Tsvangirai, who left Zimbabwe shortly after the election and has been on a regional tour to garner support, said he would return home as quickly as he could after missing his own deadline of a return by Monday.

"It's not about when it's about how," he said. "Our people are busy trying to look for some of the possible feasibilities. ... I am under their control inside the country, so as soon as they clear us, we would like to be home as soon as possible."

The MDC accuses the ruling ZANU-PF of using violence and intimidation against its supporters ahead of the run-off, which could unseat Mugabe after nearly 30 years in power.

Police said on Tuesday nine MDC activists had been arrested in the north of the country on charges of political violence.

The MDC says hundreds of its supporters have been rounded up, detained, assaulted and later released as part of a campaign it says has left over 30 people dead since the elections.

Agostinho Zacharias, the U.N. resident co-ordinator in Zimbabwe, said on Tuesday the United Nations warned of a "serious humanitarian situation" and wanted to assess the full impact of political violence after receiving reports of escalating conflict across the country.

He said the U.N. had sought permission to conduct the assessment from the government.

MDC spokesman Nelson Chamisa said, "There is selective application of the law. It is common knowledge that ZANU-PF is perpetrating political violence but there are very few cases of ZANU-PF people being arrested."

Mugabe's party denies the charges. The police say they are acting professionally, and in turn accuse the MDC of conducting a media propaganda campaign to win international sympathy.

Official results show Tsvangirai beat Mugabe in the presidential poll, but not by enough votes to avoid a run-off. In a parallel parliamentary poll, ZANU-PF lost its majority to the opposition for the first time since independence in 1980.

(Additional reporting by Cris Chinaka and Nelson Banya in Harare; Editing by Matthew Tostevin)

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