Four gunmen and two guards were killed when unidentified militants attacked an Indian Air Force base near the Pakistan border on Saturday in an apparent challenge to attempts to revive a dialogue between the nuclear-armed neighbours.

Officials said the gunmen, wearing army fatigues, managed to enter the Pathankot air base in India's northwestern state of Punjab before dawn on Saturday. Once inside, they opened fire indiscriminately.

They had earlier hijacked a police officer's car and driven it to the heavily guarded base - tactics used in earlier attacks believed to have been perpetrated by Pakistani-trained militants, Punjab's police chief Suresh Arora told Reuters.

The four gunmen and two guards were confirmed killed, according to a home ministry official.

Sporadic gunfire and helicopters flying overhead could still be heard as an operation to comb the base in search of any more gunmen continued, police said.

There was no immediate claim of responsibility for the attack.

The attack came a week after Indian Prime Minister Narendra Modi made an impromptu visit to Pakistani counterpart Nawaz Sharif, in a bid to revive bilateral talks that had previously been derailed by militant attacks.

"The moment that Modi touched down in Lahore (and probably even before), something like this was doomed to happen," said Michael Kugelman, a South Asia expert at the Wilson Center think tank in Washington.

"At this point, there's sufficient goodwill in India-Pakistan relations to weather this attack. Saboteurs won't win this one," he said.

Indian Home Minister Rajnath Singh told ANI, a Reuters affiliate: "Pakistan is our neighbor and we want peace, but any terrorist attack on India will get a befitting response."

His comments were interpreted by Indian analysts as showing restraint and indicating that New Delhi wanted to continue talks with Pakistan.(Reuters)