A rocket attack into Israel by Palestinian militants today broke a week-long Egyptian-brokered moratorium.
No one was injured by the Islamic Jihad salvo against the border town of Sderot. Israel later carried out an air strike against a rocket launcher in the northern Gaza town of Beit Hanoun.
Islamic Jihad, a relatively small faction that, like the powerful Hamas, refuses to accept co-existence with the Jewish state, had vowed revenge after Israeli troops killed four of its members in the occupied West Bank yesterday.
Hamas said such "aggression" risked killing off Cairo's mediation, seen as key to securing breathing space for there to be progress in US-sponsored peace talks between Israel and Western-backed Palestinian President Mahmoud Abbas.
Hamas, which controls the Gaza Strip and is seeking a reopening of the territory's borders as part of a truce deal, stopped short of abandoning the ceasefire talks.
It has largely held its fire since March 3rd, when Israel ended a five-day offensive against Gaza rocket crews in which more than 120 Palestinians and two soldiers died.
A spokesman for Prime Minister Ehud Olmert, said Israel would hold Hamas accountable for every rocket fired from the Gaza Strip, territory the group seized in fighting against Mr Abbas's Fatah faction in June.