Pakistan's Prime Minister Nawaz Sharif has told U.S. Secretary of State John Kerry his country is swiftly investigating who was behind last week's attack on an Indian air force base, and that it would "bring out the truth."

The assault on the base near the Pakistan border has thrown into doubt diplomatic talks planned for later this month between the nuclear-armed rivals.

Kerry, speaking to Sharif by telephone, said he hoped the attack would not derail the talks that he said were in the interests of regional security, according to a statement from the Pakistani prime minister's office late on Saturday.

"The Prime Minister told Secretary Kerry that we are swiftly carrying out investigations in a transparent manner and will bring out the truth," it said. "The world will see our effectiveness and sincerity in this regard."

A meeting between the foreign secretaries of India and Pakistan had been scheduled for Jan. 15, but it is unclear if it will still happen, after six militants launched an assault on Jan. 2 against the base and killed seven security personnel.

India has called on Islamabad to take "prompt and decisive" action against militants it blames for the assault, which only ended after a four-day operation to secure the base.

New Delhi has long accused Islamabad of supporting militant groups and helping them to launch attacks inside India, an accusation Pakistan rejects.

Indian Prime Minister Narendra Modi on Saturday visited the base, at Pathankot in the northern state of Punjab, where he was briefed on how security forces had responded to end the attack.

It remains unclear how the attackers infiltrated the fortified base, which has a 24-km (15-mile) perimeter surrounded by a 3-metre (10-foot) wall topped with concertina wire.