Israeli Prime Minister Ehud Olmert has vowed a “disproportionate” response to rocket attacks on Israel from Gaza.
He was speaking at his weekly cabinet meeting on Sunday, soon after at least two rockets hit southern Israel. No casualties were reported.
Two weeks ago, Israel and Hamas – which controls the Gaza Strip – declared separate ceasefires.
They ended Israel’s three-week assault on the Gaza Strip, which Israel said was aimed at stopping rocket attacks.
On Sunday Mr Olmert warned Israel would respond forcefully to renewed rocket fire.
“We’ve said that if there is rocket fire against the south of the country, there will be a disproportionate Israeli response to the fire on the citizens of Israel and its security forces,” he said.
One of Sunday’s rockets landed between two nursery schools in the Eshkol region of southern Israel, media reports said.
On Saturday, a rocket fired from Gaza exploded near the Israeli city of Ashkelon, with no casualties reported, and at least two were fired in the days before.
“We will not agree to return to the old rules of the game and we will act according to new rules that will guarantee that we are not dragged into an incessant tit-for-tat war that will not allow normal life in the south of the country,” Mr Olmert said.
“The situation… in recent days has increased in a manner that does not allow Israel not to retaliate in order to make sure that our position… is understood by those involved in the fire.
“The response will come at the time, the place and the manner that we choose.”
His strong stance was echoed by Foreign Minister Tzipi Livni and Defence Minister Ehud Barak.
The ceasefires, independently declared by each side, have been violated several times.
An Israeli soldier was killed in a bomb attack on the Gaza border last Tuesday. Israel responded with air raids and a brief ground incursion by soldiers and tanks.
About 1,300 Palestinians and 10 Israeli soldiers were killed in Israel’s devastating three-week assault on Gaza. Three Israeli citizens died in rocket attacks.
Israel wants the rocket attacks to end and wants to prevent militants in Gaza from being able to rearm.
Analysts say the politicians who ordered the Gaza attack also have an eye on elections on 10 February.
Hamas wants the border crossings into Gaza to be fully opened to end a 18-month blockade of Gaza which has wrecked its economy.
The Egyptians have been leading efforts to broker a permanent ceasefire by holding separate talks with officials from Israel and Hamas.