Russia called outgoing United States (US) Ambassador to Russia Jon Huntsman a professional diplomat late on Tuesday, but said he had been unable to improve battered Russia-US ties because he had been hamstrung by domestic US politics, TASS news agency reported.

Huntsman, who was appointed by US President Donald Trump in 2017, said in a resignation letter circulated by US media that he was stepping down after a two-year tenure over shadowed by US sanctions on Moscow and tit-for-tat diplomatic expulsions.

His stint in Russia came at a time when relations between Washington and Moscow hit a post-Cold War low and were strained over everything from Syria to arms control and allegations, denied by Russia, that Moscow meddled in the 2016 US presidential election to help Trump win.

“Huntsman is a professional,” TASS cited the foreign ministry as saying.

“Unfortunately, the domestic political situation in the United States did not make it possible to realise the existing potential in bilateral relations,” it said.

Huntsman, who is due to leave his post on October 3, said in his resignation letter that “we must continue to hold Russia accountable when its behaviour threatens us and our allies.”

Huntsman, a one-time Republican presidential candidate, used to chair the Atlantic Council, a Washington-based think tank that has sometimes been sharply critical of Russian domestic and foreign policy.

Russia said last month it was preparing to ban the Atlantic Council, which Russia’s prosecutor general has described as a security threat.