The Israeli army fired shells at an office of Palestinian leader Mr Yasser Arafat's Fatah movement in the northern Gaza Strip, wounding four civilians, according to witnesses and security sources.
Two shells, fired from Israeli territory, targeted a Fatah office and police station in Beit Lahia, a town near the green line separating Israel from the occupied territories, the sources said.
Two other shells fell in the area but did not explode.
Earlier four mortar shells fired by Palestinians in the Gaza Strip struck Israeli territory near a military position, without causing any casualties, a military spokesman said.
The shells landed not far from the Nahal Oz kibbutz in southern Israel, a few hundred metres from the Gaza Strip.
Other shells have fallen in recent weeks in the same sector, prompting Israeli military retaliation.
AFP