Hamas officials say all their personnel were instructed to evacuate their buildings to avoid another airstrike. - AP photo

GAZA CITY: Palestinian officials say a Hamas naval policeman has been killed and seven others have been wounded in an Israeli airstrike on their building in the northern Gaza Strip.

The Israeli military says its aircraft struck an unspecified ''terror activity site'' early Monday after Palestinian militants in Hamas-run Gaza fired a rocket at southern Israel. No one was hurt in that rocket attack Sunday evening.

The casualties were confirmed by Gaza health official Adnan Abu Salmia.

The mayor of Beit Lahiya, Izzedine Dahnoun, said an electricity transformer supplying northern Gaza from Israel was damaged by the blast, knocking out power to some 100,000 people.

Hamas officials say all their personnel were instructed to evacuate their buildings to avoid another airstrike.