Moscow (AFP) - The Russian defence ministry on Wednesday suggested the United States was supporting Islamic State jihadists, enabling them to mount counter-offensive attacks in eastern Syria.

"The main thing preventing the final defeat of ISIL in Syria is not the terrorists' military capability but support and pandering to them by American colleagues," military spokesman Igor Konashenkov said in a statement, using an alternative term for IS.

He said recent attacks on Syrian regime forces were all made "from a 50-kilometre zone around At-Tanf on the Syrian-Jordan border" where the US-led coalition is operating a garrison.

Over the past month Moscow has repeatedly accused the US of hindering the offensive in the east of the country against IS jihadists mounted by Syrian regime forces with the support of Russian airstrikes and special forces on the ground.

The military said the regime forces "neutralised mobile IS groups on the road from Palmyra to Deir-Ezzor" and freed the captured villages.

"If the US side views such operations as unforeseen 'accidents', Russian aviation in Syria is ready to begin complete eradication of all such 'accidents' in the zone they control," Konashenkov said.

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