The Israeli military said it attacked nearly all of Iran's military installations in neighboring Syria in response to an Iranian rocket barrage on Israeli positions in the occupied Golan Heights, in the most serious military confrontation between the two bitter enemies in decades.
The attack early Thursday came after Iranian forces launched 20 rockets in the direction of Israeli army units in Golan Heights and marked the largest Israeli air force strike since the Yom Kippur War of 1973.
Israeli Defense Minister Avigdor Lieberman said Israel had "hit almost the entire Iranian infrastructure in Syria," though there were reports that many of the missiles were intercepted by Syrian forces. Lieberman said Israel informed Russia and the United States ahead of the operation.
The United Nations quickly urged both sides to bring an "immediate halt to all hostile acts."
In a statement Thursday, the Russian Defense Ministry said that 28 Israeli fighter jets took part in the operation, firing more than 70 missiles. Russia, which has been the dominant military force in Syria for several years, said roughly half the missiles were knocked down by Syrian antiaircraft systems.
The Syrian army's general command said in a statement that its aerial defense systems had destroyed a "large portion of the Israeli aggression's missiles."
Iranian media described the attacks as "unprecedented."
Referring to Israel as "the Zionist entity," the state-run Syrian Arab News Agency cited a foreign ministry source who claimed Israel posed "a serious threat to international peace and security."
"This aggressive behavior by the Zionist entity," the source told the news agency, will "only lead to an increase in tensions in the area."
The Israeli army said debris from only four of the 20 rockets actually landed in Israeli territory and that the rest had fallen short.
There were no Israeli casualties, but civilian residents of communities in the entire region were awakened by air raid sirens and forced to remain in shelters for two hours.
In a briefing, the Israeli army said "dozens of targets belonging to the Iranian Quds forces in Syrian territory" were demolished in the raid, including intelligence centers, munitions storehouses and logistics sites. Israeli fighter jets, the army said, encountered stiff opposition from Syrian aerial defense systems.
A spokesman for the Syria army reported that three fighters were killed and two wounded in the Israeli strikes.
The Britain-based Syrian Observatory for Human Rights, a widely respected source, claimed 23 fighters were killed.
In a statement from Press Secretary Sarah Huckabee Sanders, the White House condemned Iran's "provocative rocket attacks from Syria against Israeli citizens" and expressed strong support for "Israel's right to act in self-defense."
"The Iranian regime's deployment into Syria of offensive rocket and missile systems aimed at Israel is an unacceptable and highly dangerous development for the entire Middle East," Sanders said.
U.N. Secretary-General Antonio Guterres, through his spokesman, expressed concern and urged "maximum restraint." U.N. peacekeepers in the Golan Heights have remained in contact with both Israel and Syria military leaders.
Prime Minister Benjamin Netanyahu, though, seemed unbowed.
"Whoever attacks us — we will attack them sevenfold and whoever prepares to attack us — we will act against them first," the prime minister said.
The nighttime skirmish exposed regional realignments that have been quietly underway for several years.
Khalid bin Ahmed Al Khalifa, the foreign minister of Bahrain, a Persian Gulf state that does not have diplomatic relations with Israel but is engaged in a power struggle with Iran, tweeted, "As long as Iran violates the regional status and uses its forces and missiles to transform states into wastelands, every country in the area including Israel has the right to defend itself and destroy the sources of danger."
Russian President Vladimir Putin appeared to have received a first-person account of Israel's position during a lightning-quick visit by Netanyahu, who returned to Israel from Moscow only hours before the Iranian barrage was launched.
In a statement, Netanyahu's office said the summit — the eighth meeting between the Russian and Israeli leaders in two years — would help preserve "continued coordination."
Russia took a cautious approach Thursday. The official state news agency TASS quoted Foreign Minister Sergey Lavrov saying "in our contacts with the Iranian leadership and the leadership of Israel, including yesterday's meeting between President Vladimir Putin and Israeli Prime Minister Benjamin Netanyahu, we emphasized the need for avoiding any mutually provoking moves."
"Both Iran and Israel have assured us that there are no such intentions," he said.
Israeli army spokesman Lt. Jonathan Conricus said he did "not yet know" if Iran's initial act was a retaliation or if it had been provoked by President Trump's announcement that the U.S. would withdraw from the Iranian nuclear deal.
Only Israel, Saudi Arabia and other Persian Gulf countries have spoken in favor of Trump's decision.
European co-signers to the nuclear pact have said they will try to salvage the deal, which freed Iran's economy from crippling economic sanctions in exchange for a 10-year freeze on Iranian uranium enrichment.
Iranian Supreme Leader Ayatollah Ali Khamenei on Wednesday expressed deep misgivings, saying, "I do not trust these countries either."
Brig. Gen. Hossein Salami, the deputy commander of the Islamic Revolutionary Guard Corps, appeared to reject the offer to salvage the nuclear deal and threatened future operations against "Iran's enemies," in a statement made to the official news agency Fars.
In a statement, Salami said Europe "cannot act independently over the nuclear deal," and that "resistance is the only way to confront these enemies, not diplomacy."
Special correspondent Tarnopolsky reported from Jerusalem. Special correspondent Nabih Boulos contributed to this report from Baghdad.
12:57 p.m.: This article was updated with additional reaction.
10:47 a.m.: This article was updated with staff reports from Jerusalem and Baghdad.
6:50 a.m.: This article has been updated with White House comment.