AGARTALA, July 29: Six paramilitary personnel were killed and an equal number of securitymen were wounded in landmine explosions in two different incidents in Tripura this months. Explosives are a new element in the operations and this change has caused serious concern to authorities. Sources claim that two outlawed organisations -National Liberation Front of Twipra (NLFT) and All-Tripura Tiger Force (ATTF) have acquired an alarming stock of explosives from foreign soil. It was not immediately known whether the explosives included the dreaded RDX. Indian intelligence agencies have definite information that a shipment of advanced arms arrived through arms dealers operating in Thailand and Myanmar. The Inter-Services Intelligence (ISI) of Pakistan played an important role in making these arms available to the insurgents, the agencies confirmed.