Imphal, July 15: Four persons, including three CRPF jawans were killed and three others seriously injured in an ambush by identified activists near Kangchip in Manipur's Imphal West district on Thursday, official sources said. The activists armed with automatic weapons ambushed three vehicles of 12th Bn CRPF coming here from Kangchup at about 0930 hours. Three jawans were killed by the shots fired by the militants during the ambush and as many seriously injured, the sources said. A civilians was also killed by a stray bullet during the exchange of fire between the activists and the CRPF, the sources said.