KABUL, Afghanistan — Six boys were killed on a swimming outing in northern Afghanistan, apparently the victims of fishermen who fired a rocket into a river, according to Afghan officials and relatives of the victims.

The suspects were identified as policemen, and six of them were arrested, including their commander, First Lt. Ahmed Farid, officials said.

The episode took place on Saturday in the village of Drumbak, in Baghlan Province, when policemen on one side of the Larkhab River fired a rocket-propelled grenade into the water. But the round went astray and exploded among a group of children bathing on the opposite shore, about 50 yards away.

Six boys, aged from 9 to 14, were killed instantly; two of them were in the shallow water near the riverbank, and the other four were on the bank. Two other children, a boy and a girl, were wounded.