UPDATE 1315 GMT: A pro-Assad blog, citing a regime “military source”, says at least 40 pro-Assad troops were killed by the alleged US airstrike near al-Bukamal.

The source said most of the casualties were regime forces, with Iraqi militia also slain.

The Assad regime is claiming an airstrike by US-led coalition warplanes on one of its military positions in eastern Syria, but US Central Command has denied the assertion.

Regime media said the strike in al-Harra, southeast of al-Bukamal on the Iraq border, caused casualties without giving details.

Unconfirmed claims said at least 38 pro-Assad militiamen were killed.

A “commander in the military alliance backing Syrian President Bashar al-Assad” — probably a label for Lebanon’s Hezbollah — told Reuters that drones, “probably American”, had bombed positions of pro-Assad Iraqi militia between regime positions and the US base at Tanf.

Major Josh Jacques, a US Central Command spokesman, knocked back the claim, “No member of the US-led coalition carried out strikes near al-Bukamal.”

The coalition maintains a 55-km (34-mile) exclusion zone around Tanf. Hezbollah and Iranian-led militia tested the zone on two occasions last year, trying to move forces inside the area, but were bombed on both occasions.

US warplanes also accidentally hit pro-Assad troops fighting the Islamic State in September 2016, killing scores. In February 2018, they attacked a pro-Assad force which tried to take positions of the US-supported, Kurdish-led Syrian Democratic Forces near a gas complex in eastern Syria. About 200 Russian “private military contractors” and other pro-Assad militia were reportedly slain.

Russia has pursued a political and propaganda campaign to press for US withdrawal from Tanf, but — despite Donald Trump’s desire for the departure of American troops — has had no success so far.

Claimed location of the strike: