We have 200 arrest warrants and hope the operation will continue for a couple of days more

Police official

The arrests came as Pakistan President Pervez Musharraf and Indian Prime Minister Atal Bihari Vajpayee attended a regional meeting in Nepal.

It was not clear if they would meet and try to defuse the tension that has been building since last month's attack by militants on the Indian parliament.

Pakistan is refusing to hand over a number of men India says were behind the parliament attack, saying it has received no evidence of their involvement.

US Secretary Colin Powell, in a BBC interview, welcomed steps taken by Gen Musharraf to defuse the crisis.

Pakistani protesters make their feelings about India clear

"I think he's done quite a bit but I expect him to do more," Mr Powell said.

The BBC's Jonathan Head says the latest arrests are a well-timed move which suggest Gen Musharraf is serious about clamping down on militant organisations.

The new wave of police detentions - focusing on the province of Punjab - began on Thursday and will continue "for a couple of days more," a Pakistani police officer said.

The detainees include members of Lashkar-e-Toiba and Jaish-e-Mohammad - the two groups India says carried out the attack on its parliament with the support of Pakistan's intelligence services.

Since the attack, in which 14 people were killed, both sides have massed thousands of troops along their border.

India says two of its troops have been killed in the latest shelling across the ceasefire line in the disputed territory of Kashmir.

If both sides are willing to talk, there will be talks

President Musharraf

The leaders of the two groups are already under detention following earlier raids.

But most of the new arrests have targeted groups accused of promoting violence between Muslims.

A Sunni group, Sipah-e-Sahaba, says 200 of its supporters were held.

Tehrik-e-Jaffria - a Shia group - estimates it has suffered 100 arrests.

The head of a Sunni seminary in the city of Faisalabad, Maulana Zahid-ul-Qasami, told the BBC a number of Islamic educational institutions affiliated to mosques have also been raided by the police.

Cautious welcome

The government of President Pervez Musharraf rounded up about 100 militants from Jaish-e-Mohammad and Lashkar-e-Toiba towards the end of December.

India welcomed that move as a "step in the right direction".

Click here for a map of the border area

But it has made it clear that its dispute with Pakistan will continue until militants are handed over.

'Willing to talk'

The opening of the South Asian Association for Regional Co-operation (Saarc) in Kathmandu was postponed until Saturday because of the late arrival of President Musharraf, whose plane was delayed by bad weather.

The possibility of conflict is causing untold anguish

Mr Musharraf, who had been on a visit to China, was forced to travel by a circuitous route because of a ban imposed by Delhi on flights by Pakistan's national airline over India.

The postponement of the summit leaves less opportunity for Indian and Pakistani leaders to meet informally to resolve their differences.

President Musharraf stressed the importance of negotiations when he finally arrived in the Nepalese capital.

"Both sides should be willing to talk," he told journalists.

"If both sides are willing to talk, there will be talks."

However, an Indian spokeswoman later said she did not think there was a conducive atmosphere for talks.

International efforts

UK Prime Minister Tony Blair - in the Indian city of Bangalore at the start of a three-day visit to the country - has urged calm between India and Pakistan.

British officials have played down any suggestion that Mr Blair might play a peace-making role in the current confrontation.

However, the United States has joined the UK in playing down the likelihood of war.

"I don't think they're going to go to war," Defense Secretary Donald Rumsfeld said.

"I think they are going to sort these things out."