Pathankot, Jan 2 (PTI): In a pre-dawn attack, a group of heavily-armed Pakistani terrorists, suspected to belong to Jaish-e-Mohammed outfit, struck at an Air Force base here in Punjab, leading to a fierce gunbattle in which three security personnel were killed along with four attackers.

The terrorists, who struck just a week after Prime Minister Narendra Modi's unscheduled visit to Lahore, could not, however, penetrate the defence cordon at the Air base which is located close to the border with Pakistan as they met with effective response from the security forces, police and security officials said.

The attack by terrorists, suspected to belong to JeM outfit, took place at around 3.30 am and three security personnel, including a Garud commando of the IAF, were killed in it, defence sources said, adding four terrorists were also killed by the security forces within five hours.

But, more terrorists were suspected to be still on the loose as gunshots were heard during the subsequent combing up operation, defence sources said.

IAF was using its two attack helicopters to assist the joint team of ground troops to neutralise the remaining terrorists, the sources said.

Authorities said helicopters and other equipment at the Air base are safe. The technical area of the Air Force station is safe, police said.

The terrorists, with huge quantity of RDX in their possession, made their way to the base from the back side where there is a jungle, they said.

But they could not go beyond the 'langar' (eating place) near the outer perimeter of the IAF complex as the security forces were ready to take them on, the sources said, about the operation which was supervised directly by National Security Adviser Ajit Doval.

Anticipating an attack after some armed men abducted an SP of Punjab Police on Thursday night, a team of NSG commandos had been rushed here last night itself after the NSA held a series of meetings with the Army Chief and top IB officials yesterday. An army detachment was also positioned at the Air base, the sources said.

Defence sources said the terrorists could not enter the technical area of the IAF station, which is the base for MiG-21 fighter planes.

Army had positioned two columns (comprising about 50 men) and a team of Special Forces at the Pathankot Air Force station prior to the attack, defence sources said. Punjab police had also been put on alert and Additional DGP had been positioned in Pathankot to oversee the security situation, the sources said.

Army, Air Force personnel, Helicopters, NSG commandos and SWAT teams had been engaged to counter the militants in the coordinated counter operation, police said. "The fierce gunbattle between terrorists and security forces went on for over five hours. However, during the combing operation fresh firing was reported and a blast was also heard," Punjab Police ADGP (Law and Order) H S Dhillon.

Top security officials in Delhi said the intent of terrorists clearly was to cause maximum destruction at the Air base which was thwarted in "one of the most successful counter-terror operations".

This was the second big terror attack in Punjab in less than a year. Three terrorists had stormed a police station in Dina Nagar in Gurdaspur in July last year before being eliminated in a 12-hour gunbattle.

The attack came just a week after Modi made an unscheduled visit to Pakistan and met Prime Minister Nawaz Sharif with an aim of improving ties.

An alarm had been sounded about today's attack yesterday after Superintendent of Police Salwinder Singh and his two associates were abducted and thrashed by 4-5 suspected Pakistani terrorists in army uniform before being dumped some distance away. They had slit the throat of the SP's friend Rajesh.

Those who attacked Salwinder Singh had also taken away his phone and used it suspectedly for making calls to Pakistan. A team of National Investigation Agency (NIA), mandated to probe terror cases, today reached Pathankot IAF base to gather inputs about the attack.

In the wake of the attack, Punjab has been put on maximum alert while security measures were also tightened in neighbouring Haryana and common capital of the two states-- Chandigarh and Himachal Pradesh, official sources said.

Security measures were beefed up at Chandigarh Air Force Stations at Chandigarh and Halwara in Punjab and at air base in Ambala.

Besides, security has also been beefed up at Army areas at Chandimandir and at Ambala cantt following terrorist attack at Pathankot.

Security at railway stations of both Punjab and Haryana had also been increased, officials said. Security was also tightened on the Pathankot-Jammu National Highway.