Two Palestinians have been killed and 10 wounded in an explosion at a northern Gaza beach. The attack early on Thursday killed a Hamas fighter and a policeman, and wounded six officers from the Palestinian coastal police, four seriously. Four other people were also wounded, hospital officials said.It was unclear where the shells came from. Palestinian officials said either Israeli navy gunboats or tanks fired the shells. Israel has denied any shelling from either sea or land. Hospital officials identified the dead Hamas fighter as Hussam Hijazi. Palestinians said Hamas fighters were operating in the area at the time.