Several Kenyans, including police officers, were shot dead by gunmen in the port city of Mombasa Monday, hours ahead of the tense opening of general elections, police said.During the night “there were attacks and shootings... police responded to a distress call and were ambushed,” said police spokesman Charles Owino, adding that police had been killed but that he could not confirm numbers. However, a police sources said at least five had been killed.