Suspected Tamil Tiger rebels killed four police in a claymore fragmentation mine ambush in Sri Lanka's restive east on Thursday, officials said, the latest in a series of attacks on the military some fear could lead to all-out war. The attack comes as Norway's special peace envoy is visiting Sri Lanka to meet the Liberation Tigers of Tamil Eelam (LTTE) and the government amid diplomatic efforts to coax the rebels to resume peace talks they pulled out of indefinitely.