The United States found itself in “humiliating isolation” at the UN, Alexei Pushkov tweeted on Sunday.
“Another blow to Washington’s credibility,” he added.
The 15-member UN Security Council on Friday voted against a US-drafted resolution to extend the arms ban on Iran.
Washington failed to receive nine votes in favor, removing the need for Russia and China to wield their vetoes which they had indicated they were prepared to do.