The Israeli army said an aircraft fired at a group that was preparing to fire a rocket into Israel.
Palestinian security sources said the group included armed men from several factions, including Hamas.
Ehud Olmert, the Israeli prime minister, rejected the possibility of a truce raised by the Palestinian prime minister, Ismail Haniya, of Hamas.
A senior government official quoted Olmert as telling his cabinet: "This is a war that cannot be on a timetable.
"There is no intention to reoccupy Gaza in order to stay there, but if certain operations are needed they will be carried out. We will operate, enter and pull out as needed."
Olmert rejected calls by the three factions that abducted Corporal Gilad Shalit, including the governing Hamas group's armed wing, to release Palestinian prisoners in exchange for information about him.
The official quoted Olmert as saying such a step would strengthen Hamas at the expense of "moderate elements" in the Palestinian Authority.
Israel Radio said militants in Gaza fired three rockets at southern Israel early on Monday, causing no casualties.
The Israeli offensive by ground and air forces has continued despite expressions of concern from the European Union and the United Nations at the worst fighting between Israelis and Palestinians since 2004 and a potential humanitarian crisis.
Israel's main ally, the United States, has been less critical.
Nicholas Burns, the US undersecretary of state, told CNN: "Let's remember who started this. It was the outrageous actions of Hamas in violating Israel's sovereignty, in taking the soldier hostage."
Early on Monday, the Israeli army said an aircraft destroyed a weapons depot belonging to the Islamic Jihad faction. Like Hamas, the group is committed to destroying Israel.
Witnesses told Aljazeera that the Israeli helicopters had bombed a workshop, not a weapons cache.