JERUSALEM, June 5 (JTA) — Confronted with a seemingly unending wave of terror, Israeli officials are searching for a response to the latest attack — this one a bombing that killed 17 people. Finding a response is becoming increasingly urgent, given warnings of a possible Palestinian “mega-attack” that will dwarf earlier attacks in terms of fatalities. Hours after a Palestinian suicide car-bombing killed 17 Israelis traveling in a bus Wednesday in northern Israel, Israeli Prime Minister Ariel Sharon convened the Security Cabinet to consider Israel’s response. As Israel vowed to retaliate, U.S. officials voiced increasing frustration with Palestinian Authority President Yasser Arafat’s failure to implement security reforms to prevent such attacks. Moreover, U.S. officials have begun hinting that they will not try to restrain Israel’s response. Along with the 17 fatalities, at least 40 people were wounded, 10 of them seriously, in the attack near the town of Megiddo. An Egged bus was traveling from Tel Aviv to Tiberias when the driver of an explosives-laden car pulled up alongside and detonated his cargo. Most of the bus passengers were Israeli soldiers. Islamic Jihad claimed responsibility for the attack, which coincided with the 35th anniversary of the start of the 1967 Six-Day War. Hezbollah television said the terrorist came from the Jenin area, which the Israeli military targeted hours after the bombing. The explosion went off just outside Megiddo Prison, where many Palestinian prisoners are held. Inmates broke into cheers at the sound of the explosion, police said. The attack came as CIA Director George Tenet held talks in the region aimed at pressing Arafat to reform the Palestinian security services, and as President Bush prepared for weekend discussions on advancing a peace initiative. The Palestinian Authority issued a condemnation of the bombing, saying it had no connection to the attack. But that did not hold back a cascade of world condemnation, including sharp criticism from the White House. Along with saying that Bush condemned the bombing “in the strongest terms,” White House spokesman Ari Fleischer said, “In the president’s eyes, Yasser Arafat has never played a role of someone who can be trusted or effective. “This attack underscores the fact that these terrorists are the worst enemies of not only the people of Israel who seek peace, but also of the Palestinian people,” Fleischer said. Meanwhile, one report quoted Tenet as telling Arafat in Ramallah on Wednesday that if terrorism continues, Arafat would have to face Sharon’s wrath alone. After the bombing, Sharon canceled meetings planned for this weekend in New York. He delayed his departure for the United States by two days, announcing that he would leave Israel on Saturday evening. Sharon will meet as planned with President Bush on June 10, then will leave Washington on June 12 to return to Israel. Along with the military operation in Jenin, which involved Israeli troops, tanks and helicopters, Israeli naval ships bombarded Palestinian targets in the Gaza Strip. Palestinians braced for a more massive reprisal. In Israel, there were growing calls for the army to reoccupy the West Bank and move against Islamic Jihad headquarters in Gaza. Given the upcoming Bush-Sharon meeting in Washington, Israeli commentators speculated that Sharon was unlikely to order a broad offensive on the scale of Operation Protective Wall, the anti-terror campaign in the West Bank launched in late March. Wednesday’s bombing occurred around 7:15 in the morning. The force of the blast flipped the bus over, and a fire left only charred, twisted remains. Police described the bomb as “very large,” estimating it contained more than 200 pounds of explosives. “I was sitting in the front, close to the driver,” said Sharon Helinger, a soldier who was lightly wounded in the attack. “The car pulled up alongside the bus, and then there was this explosion. The bus completely flipped over. When it landed, I was near the door and was able to kick it open and get out.” Israeli police officials acknowledged that heightened security measures on public transportation — including the stationing of security guards on buses — could not have prevented the car from exploding beside the bus. Israeli security officials have been warning that Palestinian terrorists may try to carry out attacks that would lead to massive casualties. One such attack — at the main gas depot in Tel Aviv on May 23 — might have caused thousands of deaths but for a technical malfunction, officials said. Another attack, in which terrorists hoped to topple Tel Aviv’s largest skyscraper by detonating a massive bomb in the parking garage, was foiled when security forces intercepted the bombers en route. Warning about new Palestinian tactics, the army spokesman, Brig. Gen. Ron Kitrey, said Wednesday that Palestinians had planned to release cyanide gas as part of a March 27 suicide bombing in Netanya — the so-called Passover Massacre — that killed 29 Israelis attending a seder. The deadly gas was not used because of technical difficulties, Kitrey added.