Israel shot down an Iranian drone that entered the country from Syria and launched a counterattack that resulted in the loss of one fighter jet, the Israeli Defense Forces announced.

The Iranian drone was shot down by a helicopter in Israel followed by a raid on the base in Syria from which the drone was operated, according to the IDF. Four Israeli F-16s struck 12 “Syrian and Iranian military targets in Syria.” The Syrians unleashed a “massive” anti-aircraft barrage, however, and one of the fighter jets crashed in Israel. It’s the sharpest confrontation yet between Iranian and Israeli forces since the beginning of the Syrian civil war.

“This is the most blatant and severe Iranian violation of Israeli sovereignty in the last years,” IDF spokesman Jonathan Conricus told reporters Saturday, per the Times of Israel. “That’s why our response is as severe as it is.”

Israel has eyed the Syrian civil war with growing alarm, as Russia and Iran’s support for Syrian President Bashar Assad has allowed the Iranian forces to spread across Syria and pose a threat to Israel. Iran denies having a military presence in Syria.

Likewise, the regime denied sending a drone into Israel. "The enemy's claims that the drone has entered the airspace of occupied Palestine are sheer lies,” the pro-Assad alliance said Saturday, according to semi-official Iranian media.

Israeli officials released video of the drone being shot down. “The Iranian drone fell in our territory and is in our possession,” Ronen Manelis, another IDF spokesman, told reporters.

Prime Minister Benjamin Netanyahu warned Russian President Vladimir Putin in January that Israel would not tolerate an Iranian military build-up in Syria. U.S. officials also have long worried that Iran would establish a land-bridge through Syria to Lebanon, where it supports Hezbollah, and thus have a substantial military presence in two countries that border Israel.

“If it is not halted on its own then we will act to stop it,” Netanyahu told reporters while traveling in Moscow. “We also spoke about Lebanon. I told [Putin] that the threat of precision weapons against Israel is a serious threat that we are not willing to accept and if we have to act, we will act.”

Iran touted the downing of the F-16 as proof of Israel’s limitations. “The era of Israeli strikes on Syria is over,” an Iranian official said, per the Times of Israel.

Russia warned Israel not to endanger any of its forces supporting Assad. "We are calling on all the involved parties to express restraint and avoid any actions, which may cause the situation’s aggravation," the Russian Foreign Ministry said, per state-run media. "We consider it necessary to respect absolutely Syria’s and the region’s other countries’ sovereignty and territorial integrity.”

Israeli officials said they don’t intend to expand the clash. “The [IDF] is ready for all scenarios, urging Iran and Syria to cease aggression,” Conricus tweeted.