An explosion ripped through a group of civilians and foreign troops in eastern Afghanistan on Wednesday, killing four children and a policeman and wounding dozens of civilians and three U.S. soldiers, officials said. The Afghan Interior Ministry said in a statement that the blast in Nangrahar province occurred when a passing police vehicle hit a mine. The ministry called it a terrorist act, implying the mine had been planted by insurgents. Buz Mohammad, the province's deputy public health chief, said four children were killed. He also told the newsmen that 43 people, most of them children, were wounded.