Prime Minister Narendra Modi received a phone call from his Pakistani counterpart Nawaz Sharif, assuring him of his support in the investigation to uncover how the lethal assault was conceived and executed.

According to a statement issued by the government, PM Modi called for "firm and immediate action against those responsible for the air base attack", based on specific and actionable information provided to Pakistan.

Seven military personnel were martyred and another 20 injured at the sprawling compound which is located just 25 km from the Pakistan border. Six terrorists have been killed.

The attack came about a week after a surprise visit by Prime Minister Narendra Modi to Pakistani counterpart Nawaz Sharif last month. India has indicated that it may delay talks in Islamabad between the foreign secretaries of the two countries that were to be held on January 15.

The head of the National Investigation Agency, Sharad Kumar, told reporters in New Delhi that the attackers came from Pakistan but did not elaborate.

The base at Pathankot has Indian Air Force MiG-21 fighter jets and attack helicopters. "I do see gaps, but security was not compromised...it will be clear after the investigation" said Defence Minister Manohar Parrikar about allegations of a series of security lapses. He toured the base today.

Among the major lapses was the delay alert sounded after a police officer's car was hijacked by the terrorists wearing army uniforms on the night of December 31. His complaint was treated as a case of armed robbery for hours. That, interrogators say, may have allowed the terrorists a large window of time to breach the base in two groups.

Phone calls made by the terrorists to their handlers were intercepted on Friday. The attack began on Saturday at dawn. Investigators are also suggesting a lack of inter-agency cooperation may have hobbled the security response.

It remains unclear exactly how the terrorists infiltrated the fortified base, which is nearly 2,000 acres large, and is surrounded by a 10-metre wall topped with barbed wire.