JERUSALEM — Israel clashed with Syrian and Iranian military forces on Saturday in a series of audacious cross-border strikes that could mark a dangerous new phase in Syria’s long civil war.
The confrontations, which threaten to draw Israel more directly into the conflict, began before dawn when Israel intercepted what it said was an Iranian drone that had penetrated its airspace from Syria. The Israeli military then attacked what it called the command-and-control center from which Iran had launched the drone, at a Syrian air base near Palmyra.
On its way back from the mission, one of Israel’s F-16 fighter jets crashed in northern Israel after coming under heavy Syrian antiaircraft fire. It is believed to be the first Israeli plane lost under enemy fire in decades.
That prompted a broad wave of Israeli strikes against a dozen Syrian and Iranian targets in Syrian territory. The Israeli military said it hit eight Syrian targets, including three aerial defense batteries, and four Iranian positions that it described as “part of Iran’s military entrenchment in Syria.”
The events, including Israel’s direct engagement with Iranian forces, threatened to intensify the crisis in Syria and showed the extent to which the country has become a battlefield between Israel and Iran, bitter foes in the region.
“This is indeed a dangerous escalation that raises the specter of direct conflict between Israel and Iran in Syria — a far more serious situation than the drawing of red lines and tit-for-tat exchanges that have occurred before,” said Robert Satloff, executive director of the Washington Institute for Near East Policy.
Forces from Russia, Turkey and the United States are also on the ground in Syria in a war with multiple fronts and multiple factions, including the remnants of the Islamic State and other Islamist militant groups.
In the past week, aircraft from three foreign countries have been brought down in the conflict: the Israeli plane; a Turkish helicopter shot down, also on Saturday, as it attacked Kurdish militias; and a Russian plane over Idlib that was bombing rebel-held territory.
Israel has long warned about the risk of conflict as Iranian forces and their allies, including Hezbollah, the Lebanese militant group militia, have dug in on Syrian territory and approached the boundary with the Israeli-held portion of the Golan Heights. Israel, which considers Iran its most potent enemy in the region, has been lobbying world powers to push these forces from the border areas.
Israel has carried out scores of strikes in Syria in recent years, largely targeting what it says are advanced weapons stores or convoys taking weapons to Hezbollah in neighboring Lebanon. Israel has also reportedly hit Syrian government facilities involved in weapons development and an Iranian base under construction in Syria.
But this was the first Israeli strike on a site where Iranian forces were present, analysts said, and Israeli military officials said this was the first time an Iranian drone had penetrated Israeli airspace during the Syrian war. There was no immediate indication that the drone was armed.
Israeli military officials accused the Syrians and Iranians of “playing with fire,” but indicated that Israel wanted to contain the situation.
“We are ready to exact a very heavy price from whoever acts against us,” said Brig. Gen. Ronen Manelis, the chief spokesman of the Israeli military, “but we are not seeking an escalation.”
The jet crash represented a severe blow to Israel’s prestige and could mark a major change after years in which it acted against targets in Syria with relative impunity.
In the past, Syria has claimed, falsely, that it had shot down Israeli aircraft. The last time an Israeli jet was downed under enemy fire appears to have been in the early 1980s.
Hezbollah said on Saturday that the downing of the Israeli F-16 jet by the Syrian Army marked the “start of a new strategic phase,” which would limit Israeli exploitation of Syrian airspace. “Today’s developments mean the old equations have categorically ended,” the Lebanese Shiite group said in a statement.
In Syria, the day’s events were viewed as potential game-changers. Government supporters celebrated in the streets of Damascus, handing out sweets and hailing Mr. Assad and the army.
This is the first time the Syrian government appears to have made good on promises to shoot down Israeli aircraft, after years of threats against both Israel and the other international militaries that have flown sorties over Syria without permission.
“I am so happy,” said Haidar, 30, a government supporter, as he handed out sweets downtown. “It makes me proud to see a Syrian response, shooting down the Israeli F-16. For years we have been waiting for a Syrian reaction against the Israeli violations and airstrikes.”
But just as Syrian self-confidence appears to have grown, Israel also sent a strong message with its broad wave of strikes on Saturday, Israeli analysts said. They noted that this was the first time in recent years Israel had struck Syrian territory in broad daylight and said that Israel had inflicted serious damage on Syria’s air-defense system. Despite more Syrian antiaircraft fire, all Israeli jets returned to base safely from the second mission, after the first jet was lost, according to the Israeli military. Syria is believed to have fired at least a dozen antiaircraft missiles, with the wreckage of one landing in Lebanon.
It was not immediately clear if the Israeli F-16 was directly hit by the Syrian antiaircraft fire. Early assessments suggested that it was, said Lt. Col. Jonathan Conricus, another spokesman for the Israeli military, though he added that nothing had been officially confirmed.
The Israeli military said two pilots had bailed from the downed aircraft “as per procedure.” One pilot was severely injured.
Prime Minister Benjamin Netanyahu of Israel spent much of Saturday in consultations with his defense minister, the Israeli chief of staff and other military officials.
Russia, along with Iran, has been helping prop up the government of President Bashar al-Assad in Syria, and the Russian Foreign Ministry issued a statement calling on “all sides involved to show restraint and avoid all acts that could lead to complicating the situation further.”
The ministry added: “It is absolutely unacceptable to create threats to the lives and security of Russian soldiers that are in the Syrian Arab Republic on the invitation of the legal government to assist in the fight against terrorism.”
After a meeting with President Vladimir V. Putin in Moscow two weeks ago, Mr. Netanyahu said in a statement that Israel viewed with “utmost gravity” Iran’s efforts to establish a military presence in Syria, and said he had made clear to Mr. Putin that Israel would “act according to need.”
Mr. Netanyahu said he spoke with Mr. Putin on Saturday and agreed that security coordination between the two countries would continue. The Israeli prime minister also said he spoke with Secretary of State Rex W. Tillerson about Saturday’s confrontation.
“The United States is deeply concerned about today’s escalation of violence over Israel’s border,” Heather Nauert, a State Department spokeswoman, said in a statement. “Iran’s calculated escalation of threat, and its ambition to project its power and dominance, places all the people of the region — from Yemen to Lebanon — at risk.”
A Pentagon spokesman, Maj. Adrian J. Rankine-Galloway, said the United States military supported Israel’s right of self-defense. “We share the concerns of many throughout the region that Iran’s destabilizing activities threaten international peace and security, and we seek greater international resolve in countering Iran’s malign activities,” Major Rankine-Galloway said in a statement.
With so many foreign forces engaged in Syria, the risks of the conflict extending beyond its borders are real, but analysts said all sides have an interest in making sure Saturday’s events do not spiral into something larger.
“I think it will be contained for the moment,” said Steven Simon, a Middle East specialist at Amherst College who was a senior official on President Barack Obama’s National Security Council. “But the situation is highly volatile,” Mr. Simon said, adding, “this has been simmering for quite a while and things are coming to a boil.”
Mr. Simon said an important question is whether the White House is counseling restraint.
“The U.S. and Israel could be thinking of their respective operations in Syria as a hammer and anvil, with Iran and its proxy forces in the middle,” he said. “If true, fighting will escalate.”
Amos Yadlin, a former chief of Israeli military intelligence and now the executive director of the Institute for National Security Studies at Tel Aviv University, said Syria, Iran and Russia would appear to have little interest now in getting into a full-blown conflict with Israel.
“Israel has the capability to destroy the Russian and Iranian project to save the Assad regime,” Mr. Yadlin said. “This is not the weak Syrian opposition. This is strong Israel.”
While Israel’s military strength is a significant factor in any response, the improving situation for the Assad government is also a consideration.
“There is no incentive for the Iranians, Syrians or Russians to draw the Israelis into a military situation that has been moving in their favor for some time,” said Stephen B. Slick, a former C.I.A. station chief in Israel who now directs the Intelligence Studies Project at the University of Texas at Austin.
The Iranian Foreign Ministry denied the drone had strayed into Israeli airspace and rejected as “laughable” reports that Israel had intercepted a drone launched from Syria.
Syrian Army officials said the drone had been carrying out a routine mission against the Islamic State, also known as ISIS or ISIL, over Syrian airspace, according to the news site Al-Manar.
Colonel Conricus insisted that the drone was “on a specific Iranian mission,” and was shot down deep in Israeli territory.
Still, some Israeli analysts did not discount the possibility that the Iranian drone had crossed into Israel because of a malfunction.
“I fail to see the logic behind the Iranians sending a drone to Israel,” said Ehud Yaari, an Israeli television analyst of Arab affairs and an Israel-based fellow of the Washington Institute for Near East Policy. “They have other priorities right now in Syria.”
But once it had crossed into Israeli airspace, the Israelis had no choice but to respond, Mr. Yaari said.
He added, “The almost constant friction between the Iranian presence in Syria and the Israeli Army is taking its toll.”