Fifteen people were wounded, including four seriously, by a Grad-model Katyusha rocket that scored a direct hit on a shopping center in Ashkelon on Wednesday - hours after US President George W. Bush arrived to celebrate the state's 60th anniversary. The rocket, fired from Beit Lahiya in northern Gaza, struck the Hutzot Mall in southern Ashkelon, causing considerable damage. Several people were initially trapped under the rubble. The four people in serious condition included a 24-year-old woman and her young daughter. In addition, 87 people were treated for shock. Earlier in the day, infantry from the Givati Brigade's Shaked Battalion, backed by tanks and Engineering Corps units, swept into southern Gaza, taking up positions on the outskirts of Khan Yunis. Five Palestinians - including two civilians, according to medical officials - were killed during the ensuing clashes. The attack on Ashkelon came as Bush was meeting with Prime Minister Ehud Olmert in Jerusalem and two days after a 69-year-old woman was killed by a Kassam rocket in Moshav Yesha. Islamic Jihad claimed responsibility for the rocket attack in a statement on its Web site. Calling the attack "entirely intolerable and unacceptable," Olmert said the government was committed to "stop it" and would "take the necessary steps so that this will stop." Olmert made his comments in a speech in Jerusalem Wednesday night at a gala event marking 60 years of US-Israeli friendship. Even before the attack, in a press statement after meeting with Bush, Olmert said Israel would not "tolerate continuous attacks on innocent civilians." "We hope that 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," the prime minister warned. Referring to the visit here earlier this week by Egyptian intelligence chief Omar Suleiman, who was trying to broker a cease-fire, Olmert said, "The fact is that while Gen. Suleiman was visiting here, Kassam rockets were still shot at innocent people in the south of Israel, and two people were killed, and this is a very threatening signal. An organization which pretends to want to stop terror can't continue to shoot at innocent people." Olmert said the cease-fire depended on Hamas's responding positively "to the principles set forth by me and by the Israeli cabinet in order to stop these operations." These principles include the release of kidnapped soldier Cpl. Gilad Schalit, the end of the arms smuggling into Gaza, and the cessation of rocket and terror attacks from the Strip. A senior diplomatic official, meanwhile, said Wednesday evening that Hamas was "overplaying its hand," and that rather than prodding Israel into accepting a cease-fire, these types of attacks were likely to push the cabinet into approving a major incursion into Gaza. "There is a war of nerves," he said. "Hamas thinks this will force Israel to accept their conditions, but I think they are misreading the country's mood." The official said that following Suleiman's visit, the balance could have gone either way regarding whether to accept the truce offer he had brought. "I think that this will push the balance toward rejecting the cease-fire," he said. Southern District Police chief Cmdr. Uri Bar-Lev said the rocket that struck the Ashkelon mall had been made in Iran. "We are familiar with this type of rocket and have dealt with them on a number of occasions in the past. We can say, unequivocally, that we know the country of origin for this rocket, which is a Grad-type Katyusha," Bar-Lev said. Bar-Lev praised the swift response of rescue services, adding that police officers had helped with some of the operations to free people trapped in the rubble. The police's Southern District command held a situation assessment on Wednesday evening following the attack; the district's alert level had already been raised. All officers have had their leave canceled, and police will increase their visible presence on Ashkelon's streets, Bar-Lev said. The rocket attack on Ashkelon came on a day when a number of officers from the city's police force were deployed in Jerusalem to help secure the visiting heads of state, including Bush, who are in the capital to celebrate Israel's 60th year of independence, Ashkelon police chief Cmdr. Haim Blumenfeld said. "Police officers from neighboring areas have been streaming in to support us," Blumenfeld said. Ashkelon police have created a rapid-rocket-response force in recent months as the city has increasingly become the target of Gazan rocket attacks. Following the rocket strike, Defense Minister Ehud Barak invited visiting US Secretary of State Condoleezza Rice to accompany him on a tour of the scene of the attack, but she declined the invitation. Barak met with Rice at Jerusalem's King David Hotel, and the two discussed a series of regional, political and security issues. Public Security Minister Avi Dichter and Industry, Trade and Labor Minister Eli Yishai visited Ashkelon to show solidarity with residents. Holding a loudspeaker, Yishai said, "We will act with all our strength, and the required [IDF ground] operation will take place." A crowd heckled the ministers, shouting, "Bring down the government!" Meanwhile, two Kadima lawmakers called on the government to kill Hamas leaders. "Hamas leaders must be assassinated. We need to prove to Bush and to the world that Israel can fight terror," said MK Shlomo Mula. Knesset House Committee chairman David Tal, also of Kadima, said "Israel must sever the hand that is launching rockets at Israel." The Likud released a statement calling for a "policy of strength" and urging the government to "topple the Hamas regime." Separately, Likud MK Gideon Sa'ar said the Ashkelon attack was the result of the government's "continuing weak policy of restraint" that he said was effectively "the abandonment of residents of the South." He called for a broad-scale military operation in Gaza "to restore security to southerners." Meanwhile, US President George W. Bush, himself in Israel as part of an official visit, expressed support for Israel in its continual fight against terror, following the attack. "We believe that the surest way to defeat the enemies...is to advance the cause of hope, the cause of freedom, liberty as the great alternative to tyranny and terror," said Bush at the "Facing Tomorrow" conference in Jerusalem - a gala event marking 60 years of US-Israeli friendship. "As we stand in peace we must understand the realities of the world in which we live," he added. "We must be steadfast and we must be strong in the face of those who murder the innocent to achieve their objectives," continued the US president. US Democratic presidential candidate Sen. Barack Obama condemned the attack. "As the United States joins Israel in celebrating its 60th anniversary, today's cowardly rocket attack and tragic injuries remind us of the ongoing threats that Israelis face with courage and resolve," he said.