The Israeli military says it hit Iranian targets around the Syrian capital Damascus.
The Israel Defense Forces said the overnight operation targeted the elite Quds Force of the Iranian Revolutionary Guards, as well as Syrian air defences.
Syrian media said most of the Israeli missiles had been destroyed by anti-aircraft fire.
Israel said it acted after the Quds Forces launched a rocket from Syria over the Golan Heights on Sunday.
It said the rocket had been intercepted.
The Israel Defense Forces (IDF) announced the start of its operation in a tweet early on Monday.
It said the Quds Force sites targeted included a munitions storage facility and a position near Damascus International Airport.
The IDF also said that “dozens of Syrian surface-to-air missiles were launched, despite clear warnings to avoid such fire”.
“In response, we also targeted several of the Syrian armed forces’ aerial defence batteries.”
Syria’s state-run Sana news agency quoted a military source as saying that the country’s air defences had shot down most of “hostile missiles”.
Witnesses in Damascus spoke of hearing loud explosions in the night sky.
The Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group, said Israeli missiles had destroyed weapons depots and military posts belonging to Iran and the Iran-backed Hezbollah movement.
The SOHR also said there had been fatalities but gave no details.
Israel rarely admits carrying out attacks inside Syria.
The operation comes after Israeli said that “a rocket was fired at the northern Golan Heights and was intercepted by the Iron Dome Aerial Defence System”.
The popular winter tourist site on Mount Hermon in the Golan Heights was closed as a result.
Israeli Prime Minister Benjamin Netanyahu issued a warning during his visit to Chad on Sunday.
“We have a set policy, to target the Iranian entrenchment in Syria, and to harm whoever tried to harm us,” he said.
Israel has expressed alarm at Iran’s deployment in Syria in support of President Bashar al-Assad, who has been battling rebel forces and Islamist groups since the start of the civil war in 2011.
In May 2018, Israel said it had struck almost all of Iran’s military infrastructure there, following a rocket attack on its positions in the Golan Heights.
Israel seized the area from Syria during the 1967 Six-Day War and later annexed it.
