Separatist rebels in India's restive northeastern state of Assam killed 43 people, mostly labourers and traders, in a series of coordinated overnight attacks, police said on Saturday. Police said heavily armed United Liberation Front of Asom (ULFA) guerrillas gunned down at least 12 people in one remote village in Tinsukia. "The massacre took place in an inaccessible area and the victims are mostly brick kiln workers and milk sellers," a senior intelligence officer told Reuters in Guwahati, the state's main city. The rebels also gunned down eight traders in a crowded market in Tinsukia's Doomduma town, police said, adding another nine people were killed in separate attacks in the district. A further 13 labourers, including a woman, were killed in two separate strikes in Dibrugarh district. "There were about 10 militants in each group and they attacked the labourers when they were preparing their dinner," V.K. Ramisetti, a senior police official in Dibrugarh, said. Another person was killed when militants triggered a blast in Sivasagar district. "Witnesses told police that attackers came with their faces covered, and they tied the hands and legs of the victims before they were shot dead," a police officer, requesting anonymity, told Reuters. The attacks forced the authorities to step up security across Assam. "Anti-insurgency operations will be intensified," Assam chief minister Tarun Gogoi told Reuters.