In the first major offensive by the Maoists in Gadchiroli district in three years, 12 Central Reserve Police Force (CRPF) personnel were killed and at least 28 injured when the rebels remote-triggered a powerful landmine in Dhanora tehsil, blowing up the mini-bus the jawans were travelling in on Tuesday afternoon. Four among those injured are critical. Officials said the exact number of personnel travelling on the bus was not immediately known and the toll could go up. The mini-bus was part of a convoy carrying troops of 192nd CRPF battalion. The landmine exploded in Dhanora, about 38km from the Gadchiroli divisional headquarters. The area — between Karwafa and Fulbodi Gatta — is considered an insurgent stronghold. The security personnel were bound for security operations when the mini-bus drove over the remote-controlled improvised explosive device. The rebels had threatened the security forces in the district with a repeat of the Laheri massacre of October 2009, in which 17 policemen were massacred. In threats issued through pamphlets, the Maoists vowed revenge for the killing of their comrades. The blast, which was heard in nearby villages, took place a day after Union rural development minister Jairam Ramesh’s visit to the district. According to intelligence inputs, Jairam is on the list of their targets. One intelligence source said that the blast could have been triggered by villagers. Senior officials have cautioned security forces about more landmines in the region. Rescue and reinforcement teams were rushed after the news of the attack reached Gadchiroli district headquarters. Security forces immediately searched the adjoining forests and launched a combing operation in the area. CRPF DG K Vijay Kumar, who is touring Maharashtra, was in Gadchiroli after he started from Nagpur on Tuesday morning, sources said, indicating that he would visit the blast site on Wednesday. According to police in Nagpur, several civilians were also injured in the blast. Two helicopters were deployed for evacuating the troops. While some injured jawans were airlifted to Nagpur and admitted to Wockhardt hospital, others were taken to Civil hospital in Gadchiroli.