HARARE, Zimbabwe - The runoff pitting President Robert Mugabe against opposition leader Morgan Tsvangirai will not take place in the next few weeks as required by law, the head of the electoral commission said in an interview published Sunday.

Tsvangirai had announced over the weekend that he would participate in a runoff against Mugabe -- but insisted the vote be held, as law requires, within 21 days of the May 2 announcement of results from the first vote.

However, the chairman of the Zimbabwe Electoral Commission said government officials need more time to prepare for the runoff.

"It was ambitious for the legislature to think 21 days would be enough," George Chiweshe was quoted by the state-run Sunday Mail as saying.

Chiweshe confirmed the 21-day electoral law, but said there are legal provisions to extend the period before the election is held. Government officials have said the electoral commission has up to a year to hold the second round.

"We want to make it clear we intend to hold the runoff at the earliest date because the period set by the legislature shows that it should be held as soon as possible," he was quoted as saying in the paper.

It took the commission more than a month to announce results from the disputed March 29 presidential election. Tsvangirai, leader of the opposition Movement for Democratic Change, maintains that he won the first round outright and claims the official figures were fraudulent.

But the opposition leader, who has remained abroad since the vote because of threats to his life, said Saturday in South Africa that he will take the risk of returning to Zimbabwe to contest a runoff.

Mugabe has been accused of orchestrating violence against the opposition since the first round, raising questions about whether a runoff would be free or fair.

Twenty-two people have died and 900 have been tortured in postelection violence, according to the Zimbabwe Association of Doctors for Human Rights. The group said 40,000 farmworkers have been displaced in an effort to prevent them from voting in the runoff.

Fifty-six opposition activists were arrested in Shamva, north of Harare, opposition lawyer Alec Muchadehama said Sunday.

The opposition accused the electoral commission of being biased toward Mugabe, and predicted that more opposition supporters would come under attack to prevent them from voting during any further delay.

Tendai Biti, secretary-general of the MDC, raised concerns about the "deepening humanitarian crisis" in Zimbabwe.

He disputed the electoral commission's claim that there were legal grounds for delaying the runoff. "They don't have the discretion to move the date," he said.

Mugabe's ruling ZANU-PF, meanwhile, already has launched its runoff campaign.

On Sunday, presidential spokesman Patrick Chinamasa said the party will not allow an opposition victory.

"Mugabe, at 84, do you believe he is fighting for himself? That's what the people of Zimbabwe should understand," he told reporters in Harare. "He is fighting blatant attempts at recolonizing Zimbabwe."

Chinamasa said the party's campaign would be based on "land, empowerment, freedom and sovereignty."

Mugabe has ruled Zimbabwe since the country gained independence from Britain in 1980 and once was hailed for promoting racial reconciliation, and bringing education and health care to the black majority.

But in recent years he has been accused of holding onto power through elections that independent observers say were marred by fraud, intimidation and rigging, and of overseeing his country's economic collapse.

Tsvangirai assured regional leaders that if he were to win the presidency, he would respect Mugabe's place in Zimbabwe's history. Tsvangirai told reporters in the Angolan capital Saturday that Mugabe would be treated as the "father of the nation" in the interest of building peace and stability in Zimbabwe.

That appeared to indicate a softening of his stance. Tsvangirai had told The Associated Press in an interview last month that he believed the Zimbabwean people would press for Mugabe to stand trial for crimes against humanity