"We are very close to a deal," but Paris is "very worried about risks that further delays could weigh on the chances", a foreign ministry spokeswoman told reporters in an apparent reference to Russia's demands for extra guarantees.

Russian Foreign Minister Sergei Lavrov has demanded written assurances from Washington that massive Western sanctions imposed on Moscow over its invasion of Ukraine will not affect its economic and military cooperation with Tehran.

US Secretary of State Antony Blinken has said such demands are "irrelevant".

Russia on Monday said that all world powers must have "equal rights" if the 2015 deal to limit Iran's nuclear programme in exchange for sanctions relief is revived.

Sanctions on Russia over its invasion of Ukraine "have nothing to do with the Iran nuclear deal", Blinken said Sunday.

France "calls on all other parties to adopt a responsible approach," the foreign ministry spokeswoman said Tuesday.

Moscow is a direct party -- along with Britain, China, France and Germany -- to the ongoing talks aimed at reviving the 2015 nuclear deal. Washington is participating indirectly.

As suspense remains over Russia's participation, Iran's official IRNA news agency said that Tehran's top negotiator Ali Bagheri would travel to Vienna early Wednesday "to continue the talks".