Police in Pakistan are mounting a massive security operation in Lahore, where opposition leader Benazir Bhutto has been placed under house arrest.

The house in which Bhutto is staying has been surrounded and hundreds of activists are reportedly being held.

The clampdown aims to stop a "long march" of protest taking place.

In response, Bhutto called for Gen Pervez Musharraf to quit as president, an increase on her demands for free elections and an end to emergency rule.

However, the BBC's Barbara Plett cautions that it remains to be seen whether Bhutto is simply expressing what she sees as the national mood or whether she is preparing for a united opposition campaign to oust the military leader.

Musharraf attracted fierce international protest when he imposed emergency rule in Pakistan on 3 November, citing rising militancy and "interference" by the judiciary in the governance of the country.

On Monday a Commonwealth meeting gave Pakistan 10 days to lift its emergency rule or face suspension.

Bundled away

Bhutto had called on her supporters to join her in a "long march" of protest against emergency rule from Lahore to Islamabad, beginning on Tuesday.

But - for the second time in five days - Pakistani police have now placed Bhutto under house arrest, saying the planned march defies emergency laws and that Bhutto's personal safety is under threat.

Vehicles, barbed wire and metal barriers surround the house where she is staying, and thousands of police are said to be on duty in Lahore.

Dozens of Bhutto's supporters who attempted to gather for the march chanted slogans, but were then bundled into police vans and driven away, our correspondent says.

Bhutto said thousands of opposition activists had been arrested across Punjab province - of which Lahore is the capital.

'Time to leave'

In interviews with the BBC, she said the Pakistani people had lost confidence in Gen Musharraf's ability to steer the country towards democracy.

"It's time for him to leave," she said.

Our correspondent says this demand apparently marks a significant shift from Bhutto.

Her demands were previously limited to calling for an end to emergency rule and demanding that Gen Musharraf relinquish his army position.

But it remains unclear if Bhutto's words will unite an opposition movement that until now has been fragmented, she adds.

Until now, neither opposition activists nor lawyers who spearheaded protests against emergency rule have participated in the protests outside Bhutto's house - reflecting their suspicions that Bhutto was still dealing with General Musharraf.

On Monday, Bhutto said her Pakistan People's Party (PPP) would hold no more talks with Gen Musharraf on a possible power-sharing deal.

Police threat

Bhutto says she still wants the 270km (170-mile) march from Lahore to Islamabad to go ahead.

But a senior police official, quoted by Reuters news agency, said: "Her residence is an official jail now.

"If they try to take the law into their own hands, then we will resort to all means necessary, including charging with batons and tear gas."

Musharraf says a parliamentary poll will be held in January, but opposition leaders want an end to emergency rule first.

On Monday, Commonwealth foreign ministers meeting in London gave Pakistan 10 days to lift its emergency rule or face suspension.

The meeting also demanded Musharraf step down as army chief and release political detainees.

Pakistan was suspended from the Commonwealth in 1999, after Musharraf seized power in a coup.

The country was reinstated in 2004.

PHOTO CAPTION

 An opposition activist shouts slogans after being arrested by police during a demonstration in Karachi. [AFP]

BBC