Moscow — The Afghan government announced an amnesty for some prisoners and called on anti-Communist guerrillas to surrender to the authorities. The Soviet news agency Tass said the amnesty, marking the fifth anniversary of Communist rule, would free certain categories of prisoners or reduce their sentences. It did not specify who. But the fighting goes on. Before the announcement, Muslim rebels attacked the military camp and power station at Afghanistan's largest dam, killing at least 15 government soldiers, Afghan rebel sources said. Following the clash at Kajaki dam, 11 government soldiers joined the guerrilla forces, the sources said.