A suicide squad of three terrorists, suspected to be from the Jaish-e-Mohammed, tried to storm the sector headquarters of the Border Security Force in Bandipora in Baramulla district on Friday.
A civilian, two terrorists and an equal number of BSF personnel were killed in the gunbattle that followed.
The terrorists entered the headquarters from the rear side at around 0945 IST and hurled grenades and opened fire on personnel working in a garage, wounding two of them, a BSF spokesman said.
They then moved towards the main gate, around 50 yards away. An alert sentry, however, shot dead two of them, the spokesman said, adding the third terrorist escaped.
The injured jawans died while being taken to hospital, he added.
The body of one of the terrorists blew up apparently due to explosives tied to the waist, he said.
The body of a civilian, who had come with milk for the establishment, was found near the main gate. He had apparently died due to a grenade blast, the spokesman said.
Combing operations are on to nab the third terrorist.
This was the first suicide attack in Jammu and Kashmir this year.
In a separate incident, terrorists on Friday morning killed a prominent People's Democratic Party activist at Drangbal Pampore village in Pulwama district.
On Thursday night, police said, militants ambushed an army patrol at Shimlar Bandipore, killing a major and a soldier.
Three soldiers were injured in the attack and shifted to a hospital. Their condition was stated to be serious.
Also on Thursday night, militants dragged a block president of the PDP and another civilian from their homes at Waripora Dangiwachi village in Baramulla district.
They slit the throat of the former, identified as Abdul Gani Malik, while the other, identified by the police as Abdul Ahad, was killed near his house.
With Inputs from Press Trust of India