Israel hit Iranian targets in a series of strikes on Sunday near the ancestral home region of Syrian President Bashar al Assad, and close to Russia's main Syrian bases on the Mediterranean coast, regional intelligence and Syrian military sources said.
The Syrian army earlier said three servicemen were killed and three were wounded in two simultaneous Israeli attacks south of the province of Tartous, and another on the capital of Damascus. It gave no details of the specific locations.
The strikes on the northeastern outskirts of Damascus hit outposts run by Lebanon's pro-Iranian Hezbollah group, two Syrian military defectors familiar with the region said.
A Syrian army officer in the Tartous coastal region told Reuters on condition of anonymity an Iranian base near the village of Abu Afsa, south of the port city was targeted alongside an air defence and radar station nearby.
Israel has staged hundreds of strikes against alleged Iranian targets in recent years, but has mostly avoided hitting the coastal provinces where Russia's main military assets are concentrated.
The latest strikes are part of an escalation of what has been a low-intensity conflict whose goal was to slow down Iran's growing entrenchment in Syria, Israeli and regional military experts say.
The strikes were close to the Russian navy's only Mediterranean base in the port of Tartous where Russian warships are docked, while Moscow's major Hmeimim air base is also in nearby Latakia province.
Russia's intervention alongside Iran helped turn the tide in favour of Assad in an over decade-old conflict.
The coastal areas are inhabited mainly by Assad's minority Alawite sect that dominates the higher echelons of power in the security force and army.
Russian forces in Syria regularly turn a blind eye to Israeli air strikes against suspected Iranian-sponsored deployments and arms transfers.
But tensions have mounted between Israel and Russia over the former's condemnation of the Ukraine war and the latter's scrutiny of a Jewish emigration agency.
Israel last month said its military jets came under Russian anti-aircraft fire over Syria in May but they missed their target, describing the confrontation as a "one-off incident.
Syria blamed Israel for major strikes on its main international airport in Damascus last June that heavily damaged runways and forced a halt for several weeks to flights.
Israeli defence officials say the civilian airport has been used regularly by Iran to transport weapons and militias.