Unidentified aircraft hit a base run by Iranian-backed militias in Syria's eastern province of Deir al Zor near the Iraqi border where Tehran has in the last year expanded its military presence, residents and military sources said on Monday.
They said the strikes were south of the town of Mayadeen along the Euphrates River which has become a major base for several Shi'ite militias, mostly from Iraq, since Islamic State militants were driven out nearly four years ago.
Iranian-backed militia fighters patrolling the streets were put on heightened alert and ambulances were seen rushing to the desert outskirts of the city after several explosions were heard, two residents said.
"Panicky militias were calling on pedestrians and cars to clear the city centre and main streets around it," Ahmad al Shawi, a resident told Reuters in a text message.
The militias now control the mainly Sunni tribal town, part of a growing presence across Deir al Zor province, residents and military sources say.
The air attacks were not immediately reported on Syrian state media, which has previously denied that thousands of Iranian-backed militia fighters are deployed across large parts of the country.
Israel, alarmed by Iran's growing regional influence and military presence in Syria, says it has carried out hundreds of strikes in Syria to slow down Iranian entrenchment.
Over the past year, strikes by unmanned Israeli aircraft have concentrated on the border town of Albu Kamal, south east of Mayadeen, that lies on a strategic supply route for Iranian-backed militias who regularly send reinforcements from Iraq into Syria.
The Iranian-backed militias are also in control of large stretches of the frontier on the Iraqi side.
Western intelligence sources say Israel has expanded air strikes on suspected arms transfers and deployments by Iranian backed militia and their Lebanese Hezbollah allies which support Syrian President Bashar al-Assad.