Troops and Tiger rebels traded artillery and mortar bomb attacks in northeastern Sri Lanka, killing at least four people on Saturday, a day after a Norwegian peace attempt failed, officials said. The rebel Liberation Tigers of Tamil Eelam (LTTE) said four civilians were killed and another 20 wounded in military attacks on the rebel-held Vakarai area. “Sri Lankan military fired artillery shells that fell in front of the Pammivedduvan school refugee camp, killing four civilians and injuring more than 10,” the Tigers said in a statement.It said another 10 civilians were wounded in a separate attack on the Patchenai school, which had been converted into refugee camp. Hundreds of civilians were unable to leave the area because of the sporadic artillery attacks, a military official in the area said by telephone.