Israeli Prime Minister Benjamin Netanyahu said his nation dealt "severe blows" to Iranian and Syrian forces following the weekend downing of an Israeli fighter jet over northern Israel.
The Prime Minister said Israel would do so again if necessary.
"We made it unequivocally clear to everyone that our rules of action have not changed one bit; we will continue to strike at every attempt to strike at us. This has been our policy and it will remain our policy."
An Israeli F-16 fighter jet was hit and went down Saturday in northern Israel after coming under "massive anti-aircraft fire" from Syrian forces, according to the Israeli army.
The incident came after an Israeli combat helicopter successfully intercepted an Iranian unmanned aerial drone that had been launched from Syria, the Israel Defense Forces said.
Both pilots aboard the Israeli jet ejected, the Israeli army said. One pilot was severely injured during the ejection, while the second was lightly wounded.
In retaliation for the downed jet, Israeli forces attacked 12 targets in Syria, including three aerial defense batteries and four targets described as Iranian, the IDF said.
An IDF statement described the four Iranian targets as "part of Iran's military establishment in Syria."
Netanyahu defended Israel's actions.
"Our policy is absolutely clear: Israel will defend itself from every attack and from every attempt to harm our sovereignty," Netanyahu said. "Iran made such an attempt today. They violated our sovereignty, they infiltrated a drone into Israel's territory from Syrian territory."
Netanyahu also spoke with Russian President Vladimir Putin on Saturday night, a key regional player and an ally of both Israel and Iran. Netanyahu reiterated Israel's willingness to defend itself, while adding that military coordination between Russia and Israel over the skies of Syria will continue.
Netanyahu also spoke with US Secretary of State Rex Tillerson, who is on his way to the region for an official visit, though he will not be stopping in Israel.
The state-run Syrian Arab News Agency reported that Syrian air defense forces had responded Saturday to what they called Israeli "aggression" by hitting more than one Israeli plane following attacks on a Syrian military base by Israeli jets.
"The Israeli enemy entity early morning at dawn conducted a new aggression against one of the military bases in the central region," SANA said, citing a military source.
IDF spokesman Lt Col Jonathan Conricus denied that more than one Israeli jet had been hit, telling CNN that one Israeli aircraft came down, with all others returning safely to base. Syria has fired anti-aircraft missiles at Israeli jets at least three times in recent months. This is the first time they have struck an Israeli jet.
The assertions by Israel regarding the downed Iranian drone "are too ridiculous to be addressed," Iranian Foreign Ministry Spokesman Bahram Qassemi said Saturday, as quoted by state-run Press TV.
"The Islamic Republic of Iran has advisory presence in Syria at the request of the country's legitimate and constitutional government," Qassemi said.
"The government and army of Syria as an independent country have a legitimate right to defend (the country's) territorial integrity and counter any type of foreign aggression."
Even as the rhetoric between long-time enemies escalated throughout the weekend, the military tension appeared to peak on Saturday afternoon, following Israel's airstrikes against the 12 targets in Syria. Since then, an uneasy quiet returned to the Israel-Syria border -- a familiar feeling in the area -- with no additional strikes or retaliations from either side.
US backs Israel
The US firmly backs Israel, with White House Press Secretary Sarah Sanders issuing a statement saying, "Israel is a staunch ally of the United States, and we support its right to defend itself from the Iranian-backed Syrian and militia forces in southern Syria."
US State Department spokeswoman Heather Nauert said in a statement Saturday that the US was "deeply concerned about today's escalation of violence over Israel's border."
"Iran's calculated escalation of threat, and its ambition to project its power and dominance, places all of the people of the region -- from Yemen to Lebanon -- at risk," Nauert said. "The US continues to push back on the totality of Iran's malign activities in the region and calls for an end to Iranian behavior that threatens peace and stability."
Meanwhile, Russia's Foreign Ministry was much more even-handed in its statement, saying that "the latest developments and attacks on Syria were viewed with serious concern" and that the losses to Syria and damage resulting from them were being examined.
"We urge all parties involved to exercise restraint and to avoid any actions that could lead to an even greater complication of the situation," the ministry said. "We consider it necessary to unconditionally respect the sovereignty and territorial integrity of Syria and other countries of the region."
Russia provides significant military backing to the Syrian government, and has not expressed concern about Iran's presence in Syria. Russia is an ally of Iran, which has sent troops and advisors to back Syrian President Bashar al-Assad. But Russia also maintains cordial ties with Israel. Given the expanded Russian presence in the region in recent years, it is Russia that is seen as having the leverage over both countries to prevent the situation from escalating further.
IDF: Drone on a mission inside Israel
Giving more details on how events unfolded, the IDF's Conricus told CNN an Iranian unmanned drone had been dispatched on a "specific mission" inside Israel.
The drone entered Israeli airspace at 4:50 a.m. local time Saturday after being tracked by the Israeli military from its launch from the Iranian T-4 command center near Palmyra, Syria, Conricus said. The IDF intercepted it with an Apache attack helicopter, he said, and the remains of the drone fell north of the Israeli town of Beit She'an.
Conricus declined to give details on the drone's presumed mission or whether it was armed. He confirmed it was the first time an Iranian drone had crossed into Israeli airspace since the start of the Syrian civil war in 2011.
In response to the drone infiltration, the IDF attacked the Iranian T-4 center with eight fighter jets, which came under significant Syrian anti-aircraft fire, Conricus said. He added that there was no Iranian or Russian anti-aircraft fire.
As the Israeli planes came under attack, one of the jets was hit. The two F-16 pilots ejected and their plane crashed in Israel's Galilee region, Conricus said. He added that the anti-aircraft missiles were likely either Russian SA-5 or SA-17 surface-to-air missiles operated by Syria.
The Israeli air force then launched its attack on 12 further targets inside Syria, Conricus said, all of which were hit.
"We are willing, prepared, and capable to exact a heavy price on anyone that attacks us. However, we are not looking to escalate the situation," Conricus posted on his official Twitter feed.
Earlier this week, the Syrian regime claimed that Israeli warplanes fired missiles from Lebanese airspace, targeting a Syrian military position in the Damascus countryside, SANA reported.
The regime said it intercepted the missiles and destroyed most of them, according to SANA.
The Israeli military declined to comment.
Tensions between Israel and Syria have escalated in recent months.
Israel has conducted numerous strikes inside Syrian borders to defend what it calls its red lines, and to prevent what it says is Iran's proxy Hezbollah -- fighting alongside the Syrian regime -- from acquiring advanced weaponry.
Authorities also accused Syria in November of violating the 1974 ceasefire agreement by "conducting construction work" in the northern part of the Golan Demilitarized Zone.