The incident came amid growing uncertainty over the health of the 86-year-old Mugabe, who failed to return to Harare Sunday from Singapore where he was undergoing medical attention.

Police Saturday burst into the offices of a small radical labour movement and arrested outspoken socialist Munyaradzi Gwisai and 46 others.

They had been attending a lecture in which speakers were debating the implications that the overthrow of Egyptian president Hosni Mubarak would have for Mugabe, said Kumbirai Mafunda, spokesman for Zimbabwe Lawyers for Human Rights. At least one of the people arrested was severely beaten, he said.

State radio reported they had been arrested for destabilising the constitutionally elected government of Zimbabwe. It quoted police spokesman James Sabau as saying that Zimbabwe would never revolt against Mugabe's government. The activists were due to appear in court soon.

Commentators have pointed out similarities between the Egyptian and Zimbabwean regimes, whose leaders, both in their 80s, have held power for about the last 30 years through repressive regimes that restricted liberties through violence.

Analysts say the anxieties of senior officials in the Harare regime over events in the Middle East are apparent in numerous warnings in the last two weeks. Defence Minister
Emmerson Munangagwa said last week that any attempt to emulate events in Egypt would be crushed.

Officials have confirmed that Mugabe flew to Singapore Feb 11 for a review of a cataract operation he underwent in January. They said he would be back in time for his 87th birthday Monday, a major date on the calendar of his ZANU(PF) party.

Scores of police offices were deployed Sunday morning on the route from Harare's airport to his home, as they usually are whenever his 30-vehicle motorcade is expected, but they were withdrawn soon after midday.

Reports in January said he had received treatment in Asia for suspected prostate cancer, but officials fiercely denied that he had received medical attention, saying he was on holiday.

Officials in the country's two-year-old power-sharing government between Mugabe and pro-democracy leader Morgan Tsvangirai have expressed anxiety over Mugabe's long absence from the country. Since he first ostensibly went on holiday in mid-December, the coalition government's cabinet has met only once. Mugabe insists that cabinet meetings can take place only with him in the chair.

There is also widespread anxiety in Zimbabwe following Mugabe's avowal that elections would be held by June, as his youth militia have gone on the rampage since then in what human rights organisations fear is the start of a wave of violent intimidation to terrorize Tsvangirai's supporters.