India's Prime Minister Manmohan Singh has vowed to take "whatever measures are necessary" to track down those responsible for the Mumbai attacks.

He said the perpetrators were based "outside the country" and India would not tolerate "neighbours" who provide a haven to militants targeting it.

Gunmen targeted at least seven sites in Mumbai late on Wednesday, killing at least 101 people and injuring 300.

An Indian general said 10-12 gunmen were still holed up at three sites.

At one, the Oberoi-Trident hotel, flames were seen rising from the roof.

Elite commandos had begun an operation to free hostages at the hotel, where dozens of people are said to remain trapped or held hostage, reports said.

A home ministry official said between 20 and 30 people at the hotel might still be hostages, while the owners said some 200 people were trapped inside.

Police earlier said hostages had been freed from another luxury hotel, the Taj Mahal Palace, but explosions and gunfire were still being heard by witnesses outside.

A stand-off continues at a Jewish centre, where an Israeli rabbi and his family are believed to have been taken hostage.

One militant reportedly phoned local TV from the centre offering to negotiate over the release of hostages.

In other developments:

• The Indian navy said it was searching ships off the west coast following reports that gunmen had arrived in Mumbai by boat
• The UK Foreign Office said a British national had died; a German, a Japanese man and an Italian are also among the dead
• The Pakistan-based militant group Lashkar-e-Toiba, which has been blamed for past b****ings in India, denied any role in the attacks

In a televised address, Mr Singh said the government "will take whatever measures are necessary to ensure the safety and security of our citizens".

He described the attacks as "well-planned and well-orchestrated... intended to create a sense of panic by choosing high profile targets and indiscriminately killing foreigners".

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The perpetrators were "based outside the country", he said, adding that they "had come with single-minded determination to create havoc in the commercial capital of the country".

India has complained in the past that attacks on its soil have been carried out by groups based in Pakistan, although relations between the two countries have improved in recent years and Pakistani leaders were swift to condemn the latest attacks.

Pakistani Foreign Minister Shah Mahmood Qureshi, in New Delhi for talks, said no-one should be blamed until investigations were finished.

"Our experience in the past tells us that we should not jump to conclusions," he told Dawn television.

Amid international condemnation of the attacks, US President George W Bush telephoned Mr Singh to offer his condolences and support.

Claim of responsibility

In the attacks late on Wednesday night gunmen, using grenades and automatic weapons, targeted at least seven sites including the city's main commuter train station, a hospital and a restaurant popular with tourists.

Police say 14 police officers, 81 Indian nationals and six foreigners have been killed.

Four suspected terrorists have also been killed and nine arrested, they add.

State police chief AN Roy earlier told local television that hostages held by the gunmen at the Taj Mahal Palace hotel - one of Mumbai's most famous hotels - had been freed.

Witnesses said civilians could be seen running from the hotel, some with suitcases. Ambulances were also reported to be arriving.

But the BBC's Mark Dummett, outside the Taj Mahal, says the situation has since become very confused, with the sounds of explosions and gunfire being heard from within the hotel, suggesting the siege is not yet over.

Earlier in the day, Indian commandos had been seen entering the hotels but there was little detail on the operation.

Meanwhile, the bosses of the Oberoi-Trident hotel say some 200 guests may still trapped in their rooms.

Earlier eyewitness reports from the hotels suggested the attackers were singling out British and American passport holders.

If the reports are true, our security correspondent Frank Gardner says it implies an Islamist motive - attacks inspired or co-ordinated by al-Qaeda.

A claim of responsibility has been made by a previously unknown group calling itself the Deccan Mujahideen. Our correspondent says it could be a hoax or assumed name for another group.