'Indirect influence'

Morozov said the economic pressure by the US through oil supply shutdown has become a tool of the new economic war with Syria, and will have an indirect influence on Russia and Iran.

He said Russia acts and will act "absolutely legally".

"We have an agreement with Syria and therefore it's up to us to decide what we supply and to whom. This will be our answer, (it is) much more effective than counter-sanctions," Morozov said.

Iran's defense minister said on Tuesday that the US sanctions have failed to slow down progress.

Diao Daming, an associate professor of international relations at Renmin University of China, said Iran has been under US sanctions for a substantial period of time, and the latest round will not have a substantive effect.

Even further sanctions are unlikely to make Iran yield, he added.

For the US government, he said, the sanctions are designed to keep putting pressure on Iran, in the hope that it will be forced back to the negotiation deal.

He said Russia, although its influence in the Middle East has not been as dominant as the US, still has some sway over countries in the region, which might make it more difficult for the US to act on its own.

The US in May abandoned the 2015 Iran nuclear deal, a move that has been criticized by the international community. The deal had removed many US and other economic sanctions over Iran, in return for Teheran's commitment to curtail its nuclear program.

Since then, the US has intensified its sanctions against Iran and has threatened more actions.

Reuters and AP contributed to this story.