The Israeli military says it believes that four Palestinians it killed in a small boat off the coast of Gaza were planning a terrorist attack.
The four who died were from al Aqsa Martyr Brigades, the military wing of Fatah, the main rival to Hamas, which governs Gaza.
The brigade says its men - who were wearing diving suits - were carrying out a training exercise, and a survivor of the attack insists they were unarmed.
But Israel, which controls the sea off the coast of Gaza and often fires warning shots at Palestinian fishing boats it considers have strayed too far from the shore, says the men were heavily armed.
Hamas does not have control over all militant groups in Gaza,.
Palestinian medical sources say four bodies have been retrieved, describing them as belonging to commandos. Hamas officials in Gaza say four bodies have been recovered and two people are missing.