Russia on Thursday dismissed the threat of US sanctions and attempts to isolate Iran, saying it intended to trade with Tehran once a UN arms embargo expires next month.
The embargo on conventional arms shipments to Iran is set to expire on October 18 after the United States failed to win support for a new UN resolution.
The administration of US President Donald Trump says it has decided to unilaterally reinstate virtually all of the UN sanctions on Iran lifted under a 2015 nuclear accord with Tehran.
Washington has said it will seek to prevent Iran from purchasing Chinese tanks and Russian air defence systems.
Speaking alongside visiting Iranian Foreign Minister Mohammad Javad Zarif, Russia's top diplomat Sergei Lavrov dismissed those threats as illegal.
"Russia will in no way build its policies on the basis of these aggressive illegal demands which have no legal force," Lavrov said.
He expressed hope that other countries cooperating with Iran would follow suit.
"The fact that the United States threatened to introduce sanctions on all those who will contradict the US interpretation of the current situation once again confirms that Washington wants to behave like a bull in a china shop," Lavrov added.
"In my opinion, the current (US) administration has lost diplomatic skills almost beyond retrieve," Lavrov said.
He added however that Russia and European countries continued talks with Washington on the subject.
Trump pulled out of the Iran deal in 2018 to the dismay of European powers. But his administration insists it is still a "participant" and can therefore go ahead with the sanctions, a position denounced by Europe as absurd.