Indian security forces killed one more gunman on Sunday at an air base attacked by militants a day earlier, leaving one assailant still suspected at large in the sprawling facility near the border with Pakistan.

Gunfire and blasts were heard as security forces hunted the lone remaining attacker in the Indian Air Force base at Pathankot, a day after the raid in which five attackers and six Indian military personnel have now been killed.

The attack by gunmen disguised as soldiers came a week after Prime Minister Narendra Modi made an unscheduled visit to Pakistani counterpart Nawaz Sharif in an effort to revive talks between the nuclear-armed neighbours.

Officials said the attack bore the hallmarks of previous suspected assaults by Pakistan-based militant groups, underscoring the fragility of recent efforts to revive bilateral talks between the often uneasy neighbours.

There was no immediate claim of responsibility.

Pakistan has condemned the attack and said it wanted to continue to build on the goodwill created by the impromptu meeting between Modi and Sharif last month.

An army official confirmed the death of the militant as the operation to secure the base - used by MiG-21 fighter jets and attack helicopters - stretched into a second day on Sunday. He did not elaborate.

Indian leaders had already praised the armed forces for their heroism in Saturday's 15-hour shootout, with Modi saying they did not let the "enemies of humanity" who attacked the base succeed.

But that appeared premature on Sunday, as the operation resumed to secure the air base in northwestern Punjab state that sprawls across an estimated 14 square km and lies just 25 km (16 miles) from the border with historic rival Pakistan.

Outside the base, rumours had circulated all morning that more gunmen were still active after Home Minister Rajnath Singh announced on Saturday that five terrorists had been "neutralised". The official body count was only four at the time.

Military trucks were seen entering and exiting the walled compound, including a demining vehicle. Dozens of security guards continued their vigil, while protesters shouted slogans and burned a Pakistani flag nearby.

One of the Indian security men killed in the attack was Subedar Fateh Singh, who won gold and silver medals in the first Commonwealth Shooting Championships held in 1995, the National Rifle Association of India said.

QUESTIONS OVER BORDER SECURITY

At least two security personnel were wounded in a blast on Sunday, a police official in Pathankot said, as troops scoured the base. One later died, according to reports that could not immediately be confirmed.

The breaching of the base's defences has raised questions about lax security on the international border in Punjab, which is a known route for drug smugglers and is less closely guarded than the disputed frontier running through Kashmir.

Most of the Indian military reported killed had retired from active service and belonged to the Defence Security Corps, a unit that staffed by veterans no longer in active service.

"The casualties were unacceptably high," said Nitin Gokhale, a defence analyst and journalist who said that intelligence on a possible attack had not been passed on in time to alert sentries at the base.

Police have said the gunmen had earlier hijacked a police officer's car and driven it to the base. It took 12 hours for information on the hijacking to be circulated, according to news reports, allowing the attackers to keep the initiative.

In New Delhi, two trains were delayed early on Sunday amid heightened security concerns after officials received information about a possible bomb threat on a train running between the capital and Lucknow to the southeast, railways spokesman Neeraj Sharma said.

Trains were deemed safe and were running on schedule by mid-morning, Sharma said. – Reuters