Two Israelis have been seriously injured in a large explosion near a Jewish settlement in southern Gaza.
The explosion targeted a military position guarding the entrance to Morag, an isolated settlement close to Gaza's southern border with Egypt.
The blast may have been caused by an explosion in a tunnel, military sources said.
Palestinian witnesses said the blast hit a military vehicle, injuring several soldiers who were evacuated by helicopter.
An Israeli commando unit had earlier made a brief incursion into Gaza City suburbs, arresting four Palestinians while air force planes provided air cover.
The planes fired on an uninhabited area to disperse armed Palestinians.
On the ground Israeli troops arrested a Hamas activist and three other wanted Palestinians before withdrawing.
In Ramallah, two Palestinians were killed in an exchange of fire with Israeli soldiers.
The two were in a house which was the target of a raid by Israeli troops.
Israeli military sources said two members of the radical Islamist movement Hamas had been killed in the village of Qarawat Banizeid, north of Ramallah.
Meanwhile, it has been announced that Mahmoud Abbas is to be sworn in as president of the Palestinian Authority at an official ceremony in Ramallah on Saturday.
Officials had initially said the ceremony would take place today.
