Raipur: Four security personnel were on Monday killed and seven others injured, including two of them critically, when Naxals blew up an anti-landmine vehicle in Chhattisgarh's Dantewada district, the fourth attack by the ultras in three days.

The blast occurred on Cholnar-Kirandul road under Kirandul police station limits when the security personnel were patrolling along a road construction route in the region this afternoon, Inspector General of Police, Bastar Range, SRP Kalluri told PTI.

The mine-protected vehicle, with 11 state police jawans aboard, was dispatched from Cholnar camp to ensure security for the construction work underway in the region, located around 450 kms away from state capital Raipur, when the rebels triggered the blast leaving four personnel dead and seven others injured, Kalluri said.

"Of the injured, two are said to be in a serious condition," he said.

Soon after the incident, reinforcement was rushed to the spot and the injured personnel were admitted to a local hospital, he said.

A combing operation has been launched in the region to nab the attackers, the IG added.

This is the fourth major attack by Naxals in the insurgency-hit state in three days. Earlier, seven STF personnel were killed and ten others injured on Saturday when Naxals ambushed them in the forests of Pidmel village in Sukma district.

The Naxals yesterday set ablaze at least 17 vehicles engaged in mining work in Kanker district. No one was hurt in the incident, police said.

A BSF jawan was killed when a group of ultras opened indiscriminate firing on security personnel, who were carrying out patrolling in the proximity of Chhote Baithiya Border Security Force camp in Kanker district late last night.