ASHKELON, Israel - A rocket fired from Gaza exploded in a shopping center in the southern Israeli city of Ashkelon on Wednesday, wounding at least 14 people, rescue officials said, just as Israel's leader was discussing the violence with visiting U.S. President George W. Bush and threatening large-scale retaliation.

The rocket ripped through the roof of the mall, causing a large chunk of the roof to collapse in a huge pile of rubble and twisted metal. Four windows were blown out of the side of the building.

By hitting a crowded shopping center in a major Israeli city just as Bush was in the country, Gaza militants significantly increased the likelihood that Israel's army chief would carry out his newly expressed desire to send large numbers of ground forces into the Hamas-ruled Gaza Strip.

A hospital official said a woman and her young daughter were seriously wounded, along with another child. Another woman was seriously wounded, and several other people were slightly wounded, said the official, Leah Malul of Barzilai Hospital in Ashkelon.

The Magen David Adom rescue service said 14 people were wounded - three seriously, two moderately and nine slightly, adding that all the casualties had been evacuated from the site of the attack, including four people who were briefly trapped under the rubble.

Two militant groups, the Iranian-backed Islamic Jihad and the Hamas-linked Popular Resistance Committees, claimed responsibility. Earlier Wednesday, five Palestinians were killed in Israeli military operations in Gaza.

A witness identified only as Yuri on Israel Radio said he was on the first floor when the rocket hit two floors above. "There was the sound of a really loud explosion. Everybody started running, it was a really big mess. I went outside and saw smoke in the air. All the windows were blown out," he said.

Army Radio said the rocket hit the third floor of the Hutzot mall. The report said a clinic takes up part of the floor. Witnesses said an early warning system meant to give a few seconds for people to take cover did not sound an alarm before the rocket slammed into the mall.

While militants have fired homemade rockets into rural southern Israeli border towns for several years, only recently have they gained the capability to target Ashkelon, a city of 110,000 people about 15 kilometers (nine miles) from the Gaza border. The longer-range attacks involve foreign-made Grad-type rockets.

Israel believes Islamic Jihad is getting the Grads from Iran. "It's part of the Iranian war against Israel," Former Deputy Defense Minister Ephraim Sneh told Israel Radio.

Speaking at a world conference marking Israel's 60th anniversary, Israeli Prime Minister Ehud Olmert said Israel will take the "necessary steps" to stop violence from Gaza and called the Ashkelon attack "intolerable and unacceptable."

"The government of Israel is committed to stop it," he said.

Speaking at the same conference, President Shimon Peres said Islamist extremists are trying to destroy Lebanon and Gaza, "but it won't work in Israel. They won't succeed in destroying Israel."

The rocket attack came as Bush was wrapping up talks in Jerusalem with Olmert. Referring to ongoing violence along Israel's southern border, Olmert blamed the militant Islamic Hamas rulers of Gaza.

"We will not be able to tolerate continuous attacks on innocent civilians," Olmert said, shortly before the rocket attack. "We hope we will not have to act against Hamas in other ways with the military power that Israel hasn't yet started to use in a serious manner in order to stop it."

Casualties have mounted recently from the daily rocket attacks by Palestinian militants on Israeli communities outside Gaza. Two people were killed in the last week. Israel has so far resisted a broad offensive, fearing heavy casualties to its soldiers.

Even before the latest hit, the Israeli military commander, Lt. Gen. Gabi Ashkenazi, changed his stand and came out in favor of a ground offensive, defense officials said. They spoke on condition of anonymity because they were not at liberty to disclose policy considerations.

Israel's high-tech military has been unable to find a way to stop the crude rockets. Past invasions have halted daily rocket fire only briefly, and the barrages resumed as soon as Israeli troops pulled out.

In parallel, Egypt has been working to mediate a truce between Israel and Hamas. In a rare hint that Israel might accept it, Olmert referred to "possible terms in what may emerge as a cease-fire" in his talks with a high-level Egyptian mediator.

Before he leaves office, Bush hopes to broker a peace agreement between Israel and the moderate Palestinian government of President Mahmoud Abbas in the West Bank.

Israel has warned it will not carry out any peace agreement until Abbas regains control of Gaza. Hamas seized control of Gaza last June from Abbas' troops.

Abbas claims the West Bank and Gaza - areas located on opposite sides of Israel - for a future independent state. Hamas, an Islamic militant group committed to Israel's destruction, opposes the peace talks.

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Associated Press writer Mark Lavie contributed to this report from Jerusalem.