A spokeswoman for the Israeli army said a helicopter gunship fired at two Palestinians, who were on a boat off the coast of Gaza, but gave no further details.
Meanwhile, a 51-year old woman was killed on Saturday during clashes between Hamas security members and Islamic Jihad group in southern Gaza, medics and Hamas said.
Hiyam Saker, a 51-year-old woman, was killed after she had been caught in the crossfire that erupted near the town of Rafah.
Eight other people were injured in the clashes that erupted in the town of Rafah. The breakdown of injuries was not immediately available.
Hamas and Islamic Jihad had different stories of why the fighting started.
Ihab al-Ghusain, a Hamas security spokesman, said the clashes erupted following a brawl between Islamic Jihad members and a Hamas supporter.
Islamic Jihad officials said the fighting began after Hamas members stopped one of their members in his car and refused to let him go.
Mutual captures followed and clashes spread around the town.
The tension in the south came as Hamas security were engaged in clashes with a large Fatah-affiliated clan in Gaza City.
Two people were killed, including a 13-year old, and at least 33 others were injured in those clashes.