Tel Aviv: Defence Minister Ehud Barak on Thursday warned that the Jewish state had no choice but to respond a day after a bombing in Jerusalem and as Gaza militants rained rockets on southern Israel.
"We have to respond," Barak said at a joint news conference with visiting US Defence Secretary Robert Gates shortly after two Grad rockets slammed into the southern port city of Ashdod.
"Israel will not tolerate these terrorist attacks and we will not allow terror to rise once again," Barak said.
Hours later, Israeli aircraft attacked four targets in the Gaza Strip, lightly wounding three people, Palestinian security sources and witnesses said.
No one was wounded in the Grad attacks which came a day after a bomb ripped through a crowded bus stop in Jerusalem, killing a British tourist and wounding 39 people, in the first such attack in the Holy City since 2004.
Meanwhile, US President Barack Obama called Israeli Prime Minister Benjamin Netanyahu on Thursday to express concern over the Jerusalem bomb attack and the rocket strikes from Gaza, the White House said.
"The President reaffirmed the United States` unwavering commitment to Israel`s security," a statement said.
Since the weekend, dozens of rockets have hit southern Israel, the vast majority fired by Islamic Jihad`s military wing the Al-Quds Brigade, who on Wednesday fired two Grads at Beersheva 40 kilometres (25 miles) away.
As tensions spiralled in and around the coastal enclave, Gaza`s Hamas rulers had on Wednesday vowed to rein in recalcitrant militant groups and restore calm.
But by Thursday afternoon, at least 11 rockets and mortar rounds had landed in southern Israel, the Army said, two of them ploughing into Ashdod, Israel`s fifth largest city with a population of more than 200,000.
Israel`s response has so far been muted, with the military launching a few air strikes and raids which have caused only limited casualties.
Barak had said Israel would respond to the assault, and insisted it would choose both the timing and the nature of its response to the rising tide of rockets, while taking care not to become "victims of our own resolution”.
"We keep the right -- how, when and in what kind of amount of firepower or munitions -- to respond," he said.
Despite anger over the attacks, Israel`s leaders appear reluctant to be dragged into another bloody war with Hamas, especially as they lack international support for any new offensive on Gaza, commentators say.
Gates said Washington firmly backed Israel`s right to respond to the both the rocket fire and the Jerusalem bomb, which he described as "repugnant acts”.
"No sovereign state can tolerate having rockets fired at its people," he said.
But he also suggested Israel should tread carefully or risk derailing the course of popular unrest sweeping Arab and Muslim countries in the region.
"We have to be mindful that we don`t want to do anything that allows extremists or others to divert the narrative of reform that is going on in virtually all of the countries in the region," Gates said.
He said that so far the mass protests, which have rocked regimes across the Middle East including Syria, have focused exclusively on domestic grievances -- not the Israel-Palestinian conflict.
Despite the latest violence and rising tensions, Gates urged both Israeli and Palestinian leaders to brave political risks and forge a peace deal.
"There is a need and an opportunity for bold action to move toward a two-state solution," he said.
Thursday`s rocket fire on Ashdod came a day after the Al-Quds Brigades vowed to fire more at cities deep inside Israel as it entered "a new phase" of resistance.
"The Al-Quds Brigade has entered a new phase of bombing targets which are further away, where thousands of Israelis live," group spokesman Abu Ahmad said on Wednesday.
And despite Hamas` pledge to rein in militants firing on Israel, Islamic Jihad`s leadership insisted it would not stop its "resistance" unless Israel did the same.
Following the threats issued by Islamic Jihad`s military wing, Palestinian security forces arrested five of the group`s senior political figures in the West Bank overnight.
They were later released after questioning, a Palestinian official said.
Grad rockets have an estimated range of up to 50 kilometres (30 miles) which could theoretically see them reaching towns immediately south of Tel Aviv.