Russia on Tuesday denied it was ready to back tougher sanctions against Iran in exchange for a new arms control treaty with the United States, the Interfax news agency reported.

A senior White House official had been quoted as saying last week that Russia could be prepared to drop its hostility to harsher sanctions against Tehran if a new Strategic Arms Reduction Treaty (START) was agreed.

"We think that such a link is completely groundless," a Russian foreign ministry source, who was not named, told the news agency.

"Any exchange between these two problems, which are utterly different in fact and format, is inadmissible.

"We see no reason to believe that in the event of progress in nuclear arms reductions negotiations with the United States, Russia would be ready to yield on the question of sanctions on Iran," the Russian diplomat said.

Media had quoted senior US arms control official Gary Samore as saying in London last week that Russia may back stronger sanctions against Iran in exchange for a new nuclear arms reduction treaty, which he said Moscow badly wanted.

US President Barack Obama and his Russian counterpart Dmitry Medvedev last week pledged to agree a new treaty to significantly reduce their nuclear arsenals. The original 1991 START agreement is due to expire in December.

The United States wants increased pressure on Tehran to dissuade it from developing atomic weapons, which Washington says is the covert aim of its nuclear drive.

But Russia -- which holds a veto on the United Nations Security Council and is helping Iran build its first nuclear power plant at Bushehr -- opposes tougher sanctions.

"It is worth pointing out that at the moment there are no ongoing discussions among the UN Security Council powers about future sanctions on Iran," the ministry source added.

The White House said Iran had been the key topic in bilateral talks between the presidents at the Moscow summit.