Israel's prime minister says the five-month truce with Hamas in the Gaza Strip has been "shattered" following 13 days of tit-for-tat attacks.
Ehud Olmert told an Israeli cabinet meeting on Sunday that he had ordered security chiefs to draw up plans to end rocket and mortar attacks on southern Israel, news agency AFP reported.
Olmert made the remarks shortly after four Palestinian fighters from the Popular Resistance Committees were killed in an Israeli air attack in northern Gaza.
Israel said the air raid had targeted Palestinian fighters who were preparing to launch rockets. Scores of rockets have landed in the south of the country in the last two weeks.
"The responsibility for the shattering of the calm and the creation of a situation of prolonged and repeated violence in the south of the country is entirely on Hamas and the other terror groups in Gaza," Olmert told Israeli ministers.
"There is no one who can criticise the Israeli government ... we cannot tolerate this price tag that the terror organisations are trying to set against our right to prevent the continuing terror attacks and threats."
Olmert said he asked Israel's security agencies to "present different action plans against the Hamas terror rule without its hampering our ability to use all necessary force in our response to violations of the calm".
An Egyptian-brokered truce between Israel and Hamas came into force on June 19 and despite sporadic violations by both sides had led to a prolonged calm until a flare-up earlier this month.
Two rockets hit uninhabited areas of Israel on Sunday without causing any casualties or damage, an Israeli army spokesman said.
"The ceasefire doesn't seem to be anything more than a name at this stage," Jacky Rowland, Al Jazeera's correspondent in Jerusalem, said.
She said the Israeli defence ministry had "made it clear if there are rocket attacks, they will attack the rocket launchers".
Senior Israeli defence sources told our correspondent there were no plans as yet for a large-scale land incursion but that the army would continue to attack fighters firing rockets into the country.
However, Ehud Barak, Israel's defence minister, told a legal conference near Jerusalem that it was possible there could be a "need for a wide-scale operation" in the near future.
"Harsh words do not equal policy," he said. "On the other hand, the military is prepared for a strong and painful operation."
Israel has stepped up its blockade of the territory by keeping border crossings closed so preventing the delivery of fuel and essential humantarian supplies, while Palestinian fighters have launched scores of rockets into southern Israel.
The Israelis have almost continuously enforced the blockade since November 5, halting the supply of United Nations food and medical aid to 750,000 Palestinians and forcing the territory's sole power plant to shut down.
Peter Lerner, Israel's liaison officer for the Palestinian territories, confirmed the border crossings remained closed on Sunday.
"Consultations on their eventual reopening will take place during the day," he said.
International organisations and human rights groups have urged Israel to ease the blockade.
UN Secretary General Ban Ki-moon "is deeply concerned at the deterioration of the humanitarian and security situation in Gaza and southern Israel. He calls on all parties to uphold international humanitarian and human rights law," a UN statement said.