By Suleiman Al-Khalidi and Angus McDowall
AMMAN/BEIRUT (Reuters) - Israeli warplanes struck a weapons supply hub operated by Lebanese group Hezbollah near Damascus airport on Thursday, targeting arms sent from Iran in commercial and military cargo aircraft, Syrian rebel and regional intelligence sources said.
The Israeli military said later that one of its Patriot anti-aircraft missile batteries intercepted a target over the Golan Heights that Israeli media described as an unmanned drone. It was the second Israeli interception of a target coming from Syria in the past few weeks.
Video carried on Arab TV and shared on social media showed the pre-dawn air strikes caused a fire around the airport east of the Syrian capital, suggesting fuel sources or weapons containing explosives were hit.
Syrian state media said Israeli missiles hit a military position southwest of the airport, but did not mention arms or fuel. It said "Israeli aggression" had caused explosions and some material losses, but did not expand on the damage.
In a sign of the heightened tensions surrounding a conflict that has already caught up regional and international powers, Damascus' ally Russia criticised the Israeli strike and said Syrian sovereignty should be respected.
Israel does not usually comment on action it takes in Syria. But Intelligence Minister Israel Katz, speaking to Army Radio from the United States, appeared to confirm involvement.
"The incident in Syria corresponds completely with Israel's policy to act to prevent Iran's smuggling of advanced weapons via Syria to Hezbollah," he said.
Prime Minister Benjamin Netanyahu had "said that whenever we receive intelligence that indicates an intention to transfer advanced weapons to Hezbollah, we will act", he added.
An Israeli military spokeswoman said: "We can't comment on such reports."
Two senior rebel sources in the Damascus area, citing monitors in the eastern outskirts of the capital, said there were five strikes on an ammunition depot used by Iran-backed militias.
Lebanon's al-Manar television, which is affiliated with Hezbollah, said early indications were that the strikes targeted warehouses and fuel tanks. It said there no casualties.
RUSSIA AND IRAN BACK ASSAD
President Bashar al-Assad is backed in Syria's six-year-old civil war by Russia, Iran and regional Shi'ite Muslim militias. These include Hezbollah, a close ally of Tehran and enemy of Israel, which describes the group as the biggest threat it faces on its borders. The two fought a month-long war in 2006.
In comments in an interview with Venezuelan television carried by the Syrian state news agency SANA, Assad said Israel was supporting terrorists with military strikes in Syria, but he made no direct mention of Thursday's attack. SANA did not say when the interview was recorded.
Syrian military defectors familiar with the functioning of the airport during the war said on Thursday that it plays a major role as a conduit for arms from Tehran.
Alongside military planes, a number of commercial cargo aircraft fly from Iran to resupply arms to Hezbollah and other groups, passing through Iraqi airspace, the defectors said.
As well as weapons, hundreds of Shi'ite militia fighters from Iraq and Iran have been flown to Damascus international airport, they said.
Intelligence sources put their numbers at 10,000 to 20,000 and say they play a significant role in military campaigns launched by the Syrian army.
Israel has largely kept out the war in Syria, but officials have consistently referred to two red lines that have prompted a military response in the past - any supply of advanced weaponry to Hezbollah, and the establishment of "launch sites" for attacks on Israel from the Golan Heights region.
Speaking in Moscow on Wednesday, where he was attending a security conference, Israeli Defence Minister Avigdor Lieberman reiterated that Israel "will not allow Iranian and Hezbollah forces to be amassed on the Golan Heights border".
Lieberman held talks with Russian Defence Minister Sergei Shoigu and Foreign Minister Sergei Lavrov, as part of efforts by Israel to coordinate with Moscow on actions in Syria and avoid the risk of confrontation.
A Defence Ministry statement said Lieberman had expressed concern to Russian ministers over "Iranian activity in Syria and the Iranian use of Syrian soil as a base for arms smuggling to Hezbollah in Lebanon".
A Western diplomat said the air strikes sent a clear political message to Iran, effectively saying it could no longer use Iraqi and Syrian airspace to resupply proxies with impunity.
Speaking to Reuters in Washington on Wednesday, Intelligence Minister Katz said he was seeking an understanding with the Trump administration that Iran not be allowed to establish a permanent military foothold in Syria.
Israeli officials estimate that Iran commands about 25,000 fighters in Syria, including members of its own Revolutionary Guard, Shi'ite militants from Iraq and recruits from Afghanistan and Pakistan.
Israel has also said that Hezbollah has built up an arsenal of more than 100,000 rockets, many of which would be capable of striking anywhere within Israeli territory. The last conflict between the two left 1,300 people dead and uprooted more than a million Lebanese and 300,000 to 500,000 Israelis.
(Additional reporting by Luke Baker and Ori Lewis in Jerusalem and Omar Fahmy in Cairo; Writing by Luke Baker, Editing by Angus MacSwan and Ralph Boulton)