CNN has reported, citing an unnamed source in the US administration that the country's intelligence was looking into several cargo flights from Iran to Syria, suspecting arms may have been transferred. The source also pointed out that those shipments took place after the US, UK and France conducted joint strikes against Syria on April 14. According to the media platform, the shipments attracted attention because they may have contained weapons that could be used against Israel in the future.
In February and April Israeli Air Forces attacked a Syrian T-4 airbase, claiming Iranian military was using it for their operations. Tel Aviv has warned that it is ready to continue its strikes if it sees a threat coming from the Iranian forces that are allegedly present in Syria. Israeli media recently published aerial photos of a Syrian airport claiming that Tehran is uses civil airlines to transfer its troops to the country. Damascus denies the presence of Iranian troops on its soil.
Several times during 2017 the Syrian and Lebanese armies reported that ammunition and armaments left on the territories liberated from Daesh* and other terrorist groups were produced by the US and its closest allies and possibly were transferred to Syria as part of shipments meant for the so-called "moderate opposition." It is also notable that Russian journalists were attacked in November 2015 by the BGM-71 TOW anti-tank missiles supplied by then US president Barack Obama to anti-Bashar Assad groups in 2014.
The joint air strikes were conducted by the UK, France and US in retaliation for the alleged chemical attack in Douma. The attack was reported by the White Helmets NGO, who has been spotted multiple times working with terrorist groups in Syria.
For its part, the Syrian government has denied the accusations, while the Russian military even dispatched a chemical corps to the alleged attack site, but failed to find any traces of the chemical weapons reportedly used as well as any patients in nearby hospitals with signs that they were affected by a poisonous substance. Moscow and Damascus has invited the OPCW to Syria's Douma to investigate the incident. Their mission has already gotten underway at the purported site of the attack.
The US, UK and France conducted their strikes prior the start of the OPCW investigation, which, according to the Russian Ministry of Defense (MoD), could have been intentional to help conceal the evidence that it was provocation conducted by the terrorist forces in Douma. Russia's MoD had warned on numerous occasions prior to the alleged attack that terrorist groups in Syria were preparing such provocations in order to blame Bashar al-Assad for them.
*Daesh (also known as ISIS/ISIL/IS) is a terrorist organization banned in Russia