Armed attackers, described by the authorities as Gazans who had crossed into Israel from Egypt, carried out multiple deadly attacks near the popular Red Sea resort of Eilat, prompting a fierce Israeli bombing raid on Gaza and threatening to escalate tensions there.

The Israeli military said it had killed at least four of the attackers in the desert near the Egyptian border and hours later it retaliated with several airstrikes on Gaza. SixPalestinians, several of them members of a militant group, were killed in the first strike, according to the group's spokesman and medical officials in Gaza.

The attack near Eilat was the deadliest in Israel since Prime Minister Benjamin Netanyahu took office two and a half years ago, and it comes at a time of great uncertainty as the Palestinians plan to seek recognition of statehood at the United Nations in the fall.

Defense minister Ehud Barak described the assault as "a grave terrorist incident" that had originated in Gaza and could probably be attributed to the "loosening" of Egypt's hold over Sinai since the revolution. Yet Israel appeared reluctant to blame the Egyptian authorities, not wanting to inflame an already delicate situation and preferring to use the events to urge more constructive Egyptian action.

"Our hope," one Israeli official said, "is that this tragedy will serve as an impetus for the Egyptians to firmly exercise their sovereignty in all of Sinai and to end the security vacuum that has started to emerge there."

In a short, televised address to the nation, Mr. Netanyahu did not mention Egypt by name and directed the blame at Gaza, which is governed by Hamas. Referring obliquely to that evening's first swift strike on the Palestinian enclave, he said, "Those who gave the order to murder our citizens, while hiding in Gaza, are no longer among the living."

Egyptian officials denied that the attackers had crossed Egyptian territory. Hamas also rejected the Israeli accusations, calling them part of a plot "meant to justify an Israeli aggression against Gaza".

Officials in Gaza said the militants killed in the Israeli airstrike belonged to the Popular Resistance Committees, a shadowy group that has worked with Hamas in the past. The group's military commander was among those killed in the strike, which hit a house in Rafah, in southern Gaza. A spokesman for the group said that three of the commander's assistants and a three-year-old boy were also killed. The group later claimed responsibility for firing three rockets at the Israeli coastal city of Ashkelon in retaliation. No one was killed in the rocket attack.

Further Israeli strikes hit Hamas training and security facilities. Officials in Gaza said a thirteen-year-old boy was killed in a house near one of the sites; Hamas had already evacuated the buildings.

Israeli analysts pointed to the group's possible connections to the multipronged attack near Eilat. "If Hamas did not give the order," said Ely Karmon of the Institute for Counter-Terrorism at the Interdisciplinary Center in Herzliya, Israel, "it must have known about plans for such a large-scale attack."

The militant attack began about midday in a sparsely populated area a few miles from Eilat and close to the border with Egypt when gunmen opened fire on an Israeli passenger bus carrying soldiers and civilians from the southern city of Beersheba to Eilat. The Israeli military said other attackers fired on a second bus and on two civilian vehicles at another point on the road, which runs along the border, and detonated a roadside bomb near Israeli soldiers who were on their way to the scene of the initial attack. Israeli officials said six of the eight Israelis killed were civilians and the other two were soldiers. The attacks unfolded over several hours, with the second of the soldiers being shot to death at nightfall.

Television images from the scene showed shattered windows and bullet holes in the first bus. The second bus, which was empty except for the driver, was a burned-out shell. Military officials said it appeared that a suicide bomber had detonated explosives alongside it. The military shut down two highways near Eilat after the attacks, complicating efforts to report from the scene.

Israel has repeatedly warned about the risks from Islamic extremists in the Sinai desert. Israel blamed the military wing of Hamas for rocket attacks last year on Eilat and the neighboring Jordanian resort of Aqaba, saying the fire came from Sinai.

eThe latest attacks threatened to create new strains in the relationship between Israel and Egypt. Tensions have grown since the Egyptian revolution that overthrew President Hosni Mubarak, a steadfast ally who helped hold in check the public's widespread sympathy with the Palestinians and loathing of Israel. His security forces had kept a close watch on the Sinai border, in part to keep out Islamist radicals who Mr. Mubarak feared could threaten his rule and in part to preserve ties with the United States and Israel. But the revolution has turned Egypt inward, ushering in a transitional government that is more concerned with the approval of its own citizens than the security of Israel, or even the threat of subversion. Egypt's new leaders have unnerved Israel by cultivating closer ties with Hamas and Iran. And while they have focused on securing Cairo, they have allowed the northern Sinai region along the Israeli border to slide into lawlessness, leaving Bedouin tribes to keep the peace. The smuggling of goods and, increasingly, migrants have surged through a network of tunnels under the Gaza border. Egypt was forced to take action recently to restore order after a police station in the regional capital of Arish was attacked by what the authorities said were Islamist militants. In the last few days, the Egyptian military has sent more than 1,000 troops to the area to apprehend the suspects. Egyptian analysts acknowledged that the lax security may well have played a role in the attacks. "The security situation in north Sinai is deteriorating, and now radical militant elements got loose," said Gamal Abdel Gawad, the director of the Ahram Center in Cairo. "It is not a remote possibility for them to cross the border and launch attacks against Israeli targets. It makes a lot of sense."