The well-coordinated strikes by small bands of gunmen starting Wednesday night left the city shell-shocked.
Late Thursday, after about 400 people had been brought out of the Taj hotel, officials said it had been cleared of gunmen. But Friday morning, army commanders said that while three gunmen had been killed, two to three more were still inside with about 15 civilians.
A few hours after that, Thamburaj, the security official, said at least one gunman was still alive inside the hotel and had cut of electricity on the floor where he was hiding. Shortly after that announcement, another round of explosions and gunfire were heard coming from the hotel.
Prime Minister Manmohan Singh blamed "external forces" for the violence - a phrase sometimes used to refer to Pakistani militants, whom Indian authorities often blame for attacks.
On Friday, India's foreign minister ratcheted up the accusations over the attacks.
"According to preliminary information, some elements in Pakistan are responsible for Mumbai terror attacks," Pranab Mukherjee told reporters in the western city of Jodhpur.
"Proof cannot be disclosed at this time," he said, adding that Pakistan had assured New Delhi it would not allow its territory to be used for attacks against India. India has long accused Islamabad of allowing militant Muslim groups, particularly those fighting in the disputed Himalayan region of Kashmir, to train and take shelter in Pakistan. Mukherjee's carefully phrased comments appeared to indicate he was accusing Pakistan-based groups of staging the attack, and not Pakistan itself.
Islamabad has long denied those accusations.
Earlier Friday, Pakistan's Defense Minister Ahmed Mukhtar, in Islamabad, denied involvement by his country: "I will say in very categoric terms that Pakistan is not involved in these gory incidents."
The gunmen were well-prepared, apparently scouting some targets ahead of time and carrying large bags of almonds to keep up their energy.
"It's obvious they were trained somewhere ... Not everyone can handle the AK series of weapons or throw grenades like that," an unidentified member of India's Marine Commando unit told reporters, his face wrapped in a black mask. He said the men were "very determined and remorseless" and ready for a long siege. One backpack they found had 400 rounds of ammunition inside.
He said the Taj was filled with terrified civilians, making it very difficult for the commandos to fire on the gunmen.
"To try and avoid civilian casualties we had to be so much more careful," he said, adding that hotel was a grim sight. "Bodies were strewn all over the place, and there was blood everywhere."
A U.S. investigative team was heading to Mumbai, a State Department official said Thursday evening, speaking on condition of anonymity because the U.S. and Indian governments were still working out final details.
India has been shaken repeatedly by terror attacks blamed on Muslim militants in recent years, but most were bombings striking crowded places: markets, street corners, parks. Mumbai - one of the most populated cities in the world with some 18 million people - was hit by a series of bombings in July 2006 that killed 187 people.
These attacks were more sophisticated - and more brazen.
They began at about 9:20 p.m. with shooters spraying gunfire across the Chhatrapati Shivaji railroad station, one of the world's busiest terminals. For the next two hours, there was an attack roughly every 15 minutes - the Jewish center, a tourist restaurant, one hotel, then another, and two attacks on hospitals. There were 10 targets in all.
Associated Press writers Ramola Talwar Badam, Erika Kinetz, Anita Chang and Jenny Barchfield contributed to this report.