India has summoned Pakistan's high commissioner to lodge a formal protest over the attacks in Mumbai.
Indian investigators said the Islamist gunmen who launched the attacks on India's financial capital last week had months of commando training in Pakistan.
India's foreign ministry said its government expected strong action to be taken against those responsible for this outrage.
Islamabad has denied involvement and warned against letting "miscreants" inflame tensions in the region.
At least 183 people were killed in the three-day siege in India's financial capital, including at least 22 foreigners.
Nine gunmen and 20 police and soldiers were also killed.
Anger mounts
The Indian government is continuing to come under fire over reports it failed to act on warnings of the deadly attacks in Mumbai.
Another top Indian politician offered to resign on Monday over the attacks, which have upset relations with nuclear rival Pakistan and undermined the government ahead of general elections due by May.
Maharashtra state chief minister Vilasrao Deshmukh, a member of the ruling Congress party, said he had offered to resign over the attacks.
Mr Deshmukh's offer follows the resignation of Indian Home Minister Shivraj Patil on Sunday, and Prime Minister Manmohan Singh's announcement of a wide-ranging overhaul of the nation's counter-terrorism capabilities.
India said it was raising security to a "war level" and had no doubt the attacks were linked to neighbouring Pakistan.
Air and sea security would be increased and India's main counter-terrorist National Security Guard would be increased in size and given more regional bases, Mr Singh said.
The attacks, which began last Wednesday, struck Mumbai's two best-known luxury hotels, the Taj Mahal and the Trident-Oberoi, and other landmarks in the city of 18 million.
Hundreds of people, many of them Westerners, were trapped or taken hostage as the gunmen hurled grenades and fired indiscriminately.
There is growing anger that warnings of an attack appear to have been missed, and the response on the first night was slow.
On Sunday, hundreds of people took to the streets of Mumbai to protest at perceived government failures, the BBC reports.
Protesters said the authorities should have been more prepared for the attacks, and also questioned whether warnings were ignored and the time it took commandos to reach the scenes of the attacks.
Pakistan denies involvement
Indian officials have said the 10 attackers who held Mumbai hostage with frenzied attacks using assault rifles and grenades came from Pakistan, a Muslim nation carved out of Hindu-majority India in 1947.
Pakistan denies any involvement, and the situation is straining improving ties between the nations.
Pakistan President Asif Ali Zardari appealed to India not to punish his country, saying militants could precipitate a war, the Financial Times reported on Monday.
Mr Zardari, whose wife, Benazir Bhutto, was assassinated by Islamist militants last year, warned that provocation by rogue "non-state actors" posed the danger of a return to war between the nuclear-armed neighbours.
Analysts say the Mumbai assaults bore the hallmarks of Lashkar-e-Taiba, a Pakistan-based group blamed for attacks in India including a 2001 parliament blast that almost plunged the two into a fourth war.
