Russia on Friday accused the United States of committing a "war crime" in Syria, saying its army had denied Syrian refugees access to humanitarian aid.

"The most severe humanitarian situation remains in the Al-Tanf region," the Russian defence ministry's Syria reconciliation centre said, referring to a garrison where US and other foreign troops train anti-Islamic State group fighters.

Tens of thousands of Syrian refugees from the Al-Rukban refugee camp on the Jordanian border are deprived of humanitarian aid because of the United States, which "illegally placed their military base there and forbids approach within 55 kilometres (35 miles) under the threat of death," the centre said.

"The actions of the US military and the so-called international coalition in Al-Tanf are a gross violation of international humanitarian law and could qualify as a war crime," it said in a statement quoted by Russian news agencies.

Earlier this month Moscow accused the US of supporting IS jihadists and enabling them to mount counter-offensive attacks in eastern Syria from near the Al-Tanf garrison.

Al-Tanf, on the key highway connecting Damascus with Baghdad, has been repeatedly menaced by a surge of Iran-backed troops loyal to Syrian President Bashar al-Assad.

Washington says the garrison is used by US and British special forces to train rebel Syrian groups fighting IS jihadists.

Russia has been flying a bombing campaign in Syria since 2015, when it stepped in to support the Assad regime and tipped the conflict in his favour.

Source: AFP