Guwahati, June 24 :    Guwahati, June 24:  Karbi militants today gunned down five ONGC employees in Assam's Karbi Anglong district after ambushing their vehicle on a hilly stretch of road near Diphu. Police said heavily armed militants of the United People's Democratic Solidarity ambushed a five-vehicle convoy that included the ONGC vehicle between Doldoli and Diphu town. All five victims, among them two engineers, died on the spot. The engineers, accompanied by two contract labourers, were headed for Diphu after a survey in Dhansiri. The ambush is believed to be in retaliation for the killing of three of the militant group's cadre by army personnel near Bokajan last night. The ONGC has always been targeted by the outfit, which has links with Naga militants. The oil and gas giant had suspended operations in Nagaland following repeated threats and had only recently announced resumption of operations. The flurry of militancy-related incidents over the past couple of days has jolted the administration. The abduction of four businessmen by militants of the National Democratic Front of Boroland in Darrang district yesterday has already sparked an exodus of non-Bodo traders from the Bodo-dominated belt. The businessmen were going from Guwahati to Tangla in Darrang district when their Tata Sumo was attacked. The driver, who was also abducted, stopped the vehicle after the militants fired at the tyres. The incident followed the abduction and killing of three traders by the same outfit at Rangapara in Sonitpur district on Friday night. The police are still clueless about the whereabouts of the abducted businessmen, though a search has been launched in the forests adjoining the India-Bhutan border. Darrang superintendent of police Khobir Ahmed told The Telegraph no outfit had contacted the families of the abducted businessmen for ransom. 'The abductors returned to search the vehicle. They were probably looking for something,' he said. Sources in Mangaldoi said the abductions have created a 'fear psychosis' in the minds of non-Bodo traders. An intelligence official said several non-Bodo traders had received extortion notices from the outfit. 'The killing of three traders in Sonitpur district on Friday was a warning to those who have not paid up,' he said. Last year, the rebels had launched a similar campaign against Bhutanese traders in the border areas. The offensive is said to be a result of the businessmen's refusal to pay 'entry tax' - for crossing the border - to the outfit.