JERUSALEM — Israeli warplanes launched a large-scale attack across the Gaza Strip on Friday, one of the fiercest in years, after a Palestinian sniper killed an Israeli soldier along the border fence during a day of escalating hostilities.
Successive explosions rocked Gaza City at nightfall and the streets emptied as warplanes struck dozens of sites that Israel said belonged to the military wing of Hamas, the Islamist group that controls Gaza.
Israeli security experts said the aerial assault was one of the most intense since a cease-fire ended 50 days of fighting in the territory in 2014. The ferocity of the bombings raised fears that the hostilities could spiral into a war, though analysts said neither side seemed eager to have an all-out conflict.
Indeed, after 1 a.m., about seven hours into the Israeli assault, a Hamas spokesman announced that the cease-fire had been restored with the mediation of Egypt and the United Nations. There was no immediate confirmation of a renewed truce from the Israeli side.
Israeli officials have denied reaching new truce agreements with Hamas after recent rounds of violence, but they have sometimes said that Israel would respond to calm with calm. There were no signs that Israel was poised for an imminent ground invasion.
Prime Minister Benjamin Netanyahu of Israel and his defense minister, Avigdor Lieberman, spent hours at military headquarters in Tel Aviv on Friday night holding emergency meetings with top officials, a highly unusual event for the start of Sabbath.
At least four Palestinians were killed by initial Israeli artillery and tank fire and in the subsequent airstrikes. Hamas said that three of the four were members of its military wing.
On the Israeli side of the border, the local authorities instructed residents to remain close to bomb shelters as they braced for possible retaliatory rocket fire from Gaza. The military this week placed batteries of its Iron Dome defense system in several locations in central Israel. But there was no immediate rocket bombardment from Gaza, signaling that Hamas may have decided to step back.
Nickolay E. Mladenov, the United Nations special coordinator in the Middle East, had urged the actors in Gaza “to step back from the brink” in a strongly worded post on Twitter on Friday night. “Not next week. Not tomorrow. Right NOW!” he wrote. “Those who want to provoke #Palestinians and #Israelis into another war must not succeed.”
Brig. Gen. Ronen Manelis, the chief spokesman for the Israeli military, blamed Hamas for escalating tensions over the past three and a half months, since the beginning of the Hamas-orchestrated mass protests along the border fence.
Speaking on Israeli television after 8 p.m., during the main evening news broadcast, General Manelis said the Israeli air assault would continue for several hours and would be “very severe.”
“We’re prepared for a broad array of scenarios and possibilities,” he said, adding, “We are determined to restore security and the sense of security to the Gaza periphery.”
By midnight, about six hours into the attack, the military said it had struck about 60 targets, many of them around three Hamas battalion headquarters in northern, southern and central Gaza. The military said the targets included weapons stores, command-and-control rooms, observation posts and a drone warehouse. Expecting Israeli retaliation for the death of the soldier, the Hamas forces had evacuated their posts ahead of time.
Lt. Col. Jonathan Conricus, another Israeli military spokesman, said it was the first time since 2014 that Israel had “taken out” active battalion headquarters. The Israeli soldier who was killed, he noted, was the first to have died in combat in the Gaza border area in the past four years.
This latest flare-up comes after months of tensions fanned by the often-violent protests along the fence dividing Israel and Gaza, during which Israeli snipers have killed more than 140 mostly unarmed Palestinians, according to Gaza health officials. The military says it has been acting to prevent breaches of the fence and to fend off attacks by Gaza militants, like the one that occurred on Friday.
The protests have since evolved into escalating exchanges of Palestinian mortar and rocket fire against Israeli positions and civilian border communities, and waves of Israeli airstrikes against Hamas targets in Gaza.
Israelis’ nerves have also been frayed by a plague of wildfires set by flaming kites and balloons launched from Gaza into southern Israel, which have charred large tracts of woodland and farmland. One flaming balloon landed in the yard of an Israeli kindergarten this week. It caused no damage or injuries.
Nevertheless, there has been increasing talk of war in recent days, with Israeli leaders warning Hamas that they would not tolerate a continuation of the arson attacks.
The friction had already led to two recent bursts of conflict, which ended with hurried efforts by Egypt to restore the cease-fire. In one such episode last weekend, two Palestinian youths were killed in an Israeli airstrike on an otherwise empty shell of a building used by Hamas as a training site, and four Israelis were wounded as more than 100 mortar shells and rockets were launched from Gaza.
Israel and Hamas had seemed determined to deter each other from further action. Fawzi Barhoum, the Hamas spokesman, said on Friday that “bombing will be met with bombing, and sniping will be met by sniping.” Hamas vowed to avenge the death of one of its militants on Thursday from Israeli shelling in Rafah in southern Gaza.
Ehud Yaari, an Israeli television analyst and a fellow of the Washington Institute for Near East Policy, said Hamas was “interested in maintaining a controlled level of confrontation with Israel” to press its broader demands for assistance for Gaza, an impoverished and isolated coastal enclave.
The armed, low-intensity skirmishes between Hamas and Israel in recent weeks were intended by both sides not to kill, Mr. Yaari said. “It got out of hand, igniting this cycle,” he added.
Mr. Yaari said Israel’s next moves would largely depend on Hamas. If Hamas did not unleash heavy barrages of rocket fire, he said, there was a good chance that the current confrontation would be contained.
Israel has other military priorities for now, with tensions growing in the north. President Bashar al-Assad’s forces are poised to regain control of the Syrian side of the Golan Heights, and oust rebel insurgents from the areas just beyond Israel’s northern frontier.
Still, Hamas has become increasingly frustrated. Israel has been using new technologies to systematically destroy Hamas’s network of tunnels beneath the fence, one of its main military assets and one in which it has invested heavily.
And instead of the fence protests pressuring Israel to ease its tight control of the movement of people and goods in and out of Gaza, Israel has clamped down with even harsher economic sanctions.
Mr. Barhoum, the Hamas spokesman, had said earlier on Friday that the marches on the border would continue, aimed at breaking the Israeli blockade.
“Our people won’t be broken,” he said, “no matter what the sacrifices.”
Iyad Abuheweila and Ibrahim El-Mughraby contributed reporting from Gaza City.