Jorhat, Jan. 22: All police stations in the five districts of Upper Assam, especially those adjacent to Nagaland and Arunachal Pradesh, have been put on high alert following an attack by Ulfa's Paresh Barua faction on Namtola police station in Sivasagar district, bordering Nagaland, late last night.

A policeman was injured and four vehicles damaged in the attack.

Police sources said a group of about five militants, armed with AK-series rifles, fired indiscriminately at the police station from a distance of about 100 metres around 10.55pm, taking cover behind a pile of pebbles and sand on the road in front of a house across the police station.

Sivasagar superintendent of police A.K. Singh told this correspondent today that one of the bullets ricocheted off a wall of the sentry post and hit constable Leeladhar Chetia who was on duty there. Chetia, who was shifted to Assam Medical College and Hospital, Dibrugarh, is said to be out of danger.

Singh said the police personnel at the station retaliated and chased away the militants, who manoeuvred the lanes of the residential area and crossed the border into Nagaland, a distance of 300 metres from the police station. Namtola is also about 12km from Sonari, headquarters of Charaideo subdivision, and 60km from the district headquarters of Sivasagar. Combing operations are on along the border and the adjoining Abhaypur reserve forest, he added.

As they fled, the militants triggered an improvised explosive device (IED) they had planted on a mini-truck parked inside a nearby garage. Its engine blew up, severely damaging the truck and three other vehicles ' a Maruti van, a Maruti Alto and an auto-rickshaw ' parked nearby.

Deputy inspector-general of police (eastern range) P.C. Saikia, who visited the police station today, told The Telegraph that as the inter-state border was so near that militants could cross it easily.

Both Saikia and Singh said the police took extreme caution to prevent any kind of loss of civilian lives in the thickly populated area. "Our policemen chased them and exercised restraint to avoid civilian casualties as the group fled though lanes in the area congested with shops and residences," the DIG said.

Saikia said he had asked all police stations and outposts, especially those located in the remote areas of the hilly terrain along the inter-state boundary, to be on maximum alert given intelligence reports that rebels are trying to "create trouble" in the run-up to Independence Day.

Three districts of Upper Assam, Sivasagar, Jorhat and Golaghat, share a 350km boundary with Nagaland. The other two districts of Upper Assam, Dibrugarh and Tinsukia, along with Sivasagar share a 300km boundary with Arunachal Pradesh.

Militants are believed to have transit camps/shelters in the neighbouring states following Ulfa's understanding with rebel outfits operating in Nagaland and in a few districts of Arunachal Pradesh having Naga population.

In a statement issued today by Aranya Asom, a member of the publicity wing of the Paresh Barua group, the outfit claimed responsibility for the attack. It said the action was in retaliation to the killing of an innocent youth, Lalit Moran, in Tinsukia district on Sunday by security forces.