There were no casualties or damage reported, though one of the rockets landed near a kindergarten in a community near Gaza, police spokesman Micky Rosenfeld said. Warning sirens sent residents scrambling for shelter.
The Israeli offensive was aimed at halting years of rocket attacks, and the military declared a cease-fire on Jan. 18 after saying its goals had been achieved.
But Sunday's rockets, which followed sporadic rocket fire and the killing of an Israeli soldier in a border bombing attack last week, illustrated the difficulties of achieving a complete end to the attacks. Despite years of efforts, Israel's high-tech military still has not found a solution to stopping the crude, homemade projectiles.
Speaking to his Cabinet on Sunday, outgoing Prime Minister Ehud Olmert said Israel would respond "when and where we choose."
The government's position, Olmert said, is that "if there is shooting at residents of the south there will be an Israeli response that will be harsh and disproportionate by its nature to the shooting at residents of Israel and at our forces."
Hamas has not taken responsibility for any of the new attacks, which have been claimed by smaller militant groups. But Israel says it holds Hamas, which has ruled Gaza since seizing power in June 2007, responsible for all attacks emanating from Gaza.
The rocket strikes come just over a week before Israel's parliamentary elections, and they could influence the outcome by making the Gaza offensive appear less successful. That could erode support for candidate Tzipi Livni, the foreign minister and one of the leaders behind the operation.
Livni has replaced Olmert as head of the centrist Kadima party and is the only serious challenger to the front-runner, hardline Likud leader Benjamin Netanyahu, according to recent opinion polls.
Netanyahu has been campaigning on a hardline platform that calls for a tough stance against Hamas, and he stands to benefit if Israelis conclude that the offensive failed to achieve its goal of making residents of southern Israel safer.
Since ending the offensive, Israel has conducted retaliatory strikes and pounded tunnels Hamas uses to smuggle in weapons from Egypt. Israeli forces have also shot and killed three men who Palestinians identified as farmers along the Gaza-Israel border.
One of Israel's main concerns is that Hamas could continue smuggling weapons into Gaza through tunnels under the Egypt border. The smuggling allowed the group to obtain longer-range rockets that now have about one-eighth of Israel's population in range.
Israel is pushing Egypt to do more to crack down on the flow of weapons, and internationally backed anti-smuggling efforts are at the center of attempts to win a lasting cease-fire in Gaza.
On Sunday morning, AP Television News footage in the border town of Rafah showed surveillance cameras mounted on the roof of a house on the Egyptian side. An Egyptian soldier was visible on the balcony, looking into Gaza with binoculars. The equipment apparently had been recently installed.
It was unclear if the equipment was part of a new effort by Egypt to stop smuggling. Israeli defense officials say contacts between Israel and Egypt have been stepped up since the Gaza offensive, but Egyptian security officials would not confirm that new efforts were under way.
Gaza is still struggling to recover from the punishing three-week offensive, which left swaths of the territory damaged and nearly 1,300 people dead, more than half of them civilians, according to Gaza officials. Thirteen Israelis were killed, including three civilians.
By Associated Press Writer Matti Friedman