Indian commandos are storming a Jewish centre in Mumbai, where gunmen are holding a number of people hostage.
TV footage showed troops abseiling from a helicopter to take the roof of the Chabad Lubavitch centre, while forces on the ground entered the building.
Security forces are also clearing gunmen from two luxury hotels, more than a day after a series of attacks that killed 119 people and injured 300. Indian Prime Minister Manmohan Singh vowed to track down the perpetrators.
Gunmen armed with automatic weapons and grenades targeted at least seven sites in Mumbai late on Wednesday, opening fire indiscriminately on crowds at a major railway station, the two hotels, the Jewish centre, a hospital and a cafe frequented by foreigners.
The attacks are the worst in India's commercial capital since nearly 200 people were killed in a series of bombings in 2006. On Thursday, the Indian prime minister said the government would "take whatever measures are necessary to ensure the safety and security of our citizens".
Mr Singh said the attackers were based "outside the country" and that India would not tolerate "neighbours" who provide a haven to militants targeting it. 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.
Eyewitnesses at the hotels said the attackers were singling out British and American passport holders, which our security correspondent Frank Gardner says implies an Islamist motive - attacks inspired or co-ordinated by al-Qaeda.
Co-ordinated, mass casualty attacks that target civilians and undefended buildings are very much in the al-Qaeda mould, and the apparent singling out of Westerners also points to a global Jihadist agenda.
He says al-Qaeda are also acutely media-savvy, filming their attacks and in the case of hostages, sometimes murdering them on camera.