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Pathankot, India • Suspected militants infiltrated an Indian air force base near the border with Pakistan and fought security forces for hours, leaving at least four gunmen and two members of India's security forces dead.

The attack Saturday at the Pathankot air force base in Punjab came just a week after the first visit to Pakistan in 12 years by an Indian prime minister. Police said they were investigating whether the gunmen came from the Indian portion of Kashmir, where rebels routinely stage attacks, or from Pakistan.

The assault began a couple of hours before dawn when a group of gunmen entered the section of the base where the living quarters are located, the Defense Ministry said. But the attackers were unable to penetrate the area where fighter helicopters and other military equipment are kept, it said.

By late morning it appeared that the violence had ended with the killing of the gunmen by Indian forces. But two hours later, more gunfire erupted and an air force helicopter was seen firing on an area of the base, about 267 miles north of New Delhi.

Air force spokeswoman Rochelle D'Silva said Saturday night that troops were combing the entire base to fully secure it. By 9 p.m., no gunfire had been heard around the base for more than three hours.

Indian Prime Minister Narendra Modi made an unannounced visit to Pakistan on Dec. 25 to meet with his Pakistani counterpart, Nawaz Sharif. The visit was seen as a potential sign of thawing relations between the two nuclear-armed neighbors. The two leaders also held an unscheduled meeting at the Paris climate change talks last month.

The Indian Defense Ministry said there had been intelligence reports about a likely terror attack on military installations in Pathankot, and that the air force had been prepared to thwart any attackers.

"Due to the effective preparation and coordinated efforts by all the security agencies a group of terrorists were detected by the aerial surveillance platforms as soon as they entered the Air Force Station at Pathankot," the ministry said in a statement.

Pathankot is very close to India's border with Pakistan. The Himalayan region of Kashmir, where rebels have been fighting since 1989 for independence or merger with Pakistan, is divided between India and Pakistan, but is claimed in its entirety by both.

India accuses Pakistan of arming and training Kashmir's insurgents, a charge Pakistan denies.

Pakistan's Foreign Ministry condemned the attack. "Building on the goodwill created during the recent high level contacts between the two countries, Pakistan remains committed to partner with India as well as other countries in the region to completely eradicate the menace of terrorism afflicting our region," it said in a statement.