With the parties to the Iran agreement, which the US abandoned in 2018, now seemingly close to a new accord, Blinken rejected fresh demands voiced Saturday by Russian Foreign Minister Sergei Lavrov.

The sanctions on Russia over its invasion of Ukraine "have nothing to do with the Iran nuclear deal," Blinken said on CBS talk show "Face the Nation."

They "just are not in any way linked together, so I think that's irrelevant," he said, speaking from Moldova, a small country on Ukraine's southwest border.

Blinken added it was not only in America's interest but Russia's as well that Iran not be able "to have a nuclear weapon or the capacity to produce a weapon on very, very short order."

- 'Pragmatic approach' -

The latest Russian reservations, coming amid the intense crisis over Ukraine, threaten hopes that an Iran agreement could be wrapped up quickly.

Iran and the United Nations nuclear watchdog had announced tentative agreement early Saturday on an approach for resolving issues crucial to reviving the country's 2015 nuclear accord with world powers.

Rafael Grossi, chief of the International Atomic Energy Agency (IAEA), said in Vienna that while the UN agency and Iran had yet to settle "a number of important matters," they had now "decided to try a practical, pragmatic approach" to overcome them.

However, Grossi said there was "no artificial deadline."

Both US and British officials said late in the week that negotiators in the Vienna talks were close to a possible deal, while cautioning that some issues remained to be settled.

But Lavrov said Saturday that Moscow, itself slapped with severe sanctions over its invasion of Ukraine, needed guarantees from Washington before backing the nuclear deal.

He said Russia wanted written guarantees that Ukraine-related sanctions "will not in any way harm our rights to free, fully fledged trade and economic and investment cooperation, military-technical cooperation with Iran."

Russia is party to the Vienna talks along with Britain, China, France and Germany. The United States is participating indirectly.

Moscow is expected to play a role in implementing any fresh deal with Iran, for example by receiving shipments of enriched uranium from Iran.

The 2015 nuclear deal has been hanging by a thread since then US president Donald Trump pulled out in 2018 and reimposed sweeping sanctions, including on Iranian petroleum exports.

- 'Very damaging' -

The landmark accord was aimed at guaranteeing Tehran could not develop a nuclear weapon -- something it has always denied wanting to do.

Iran said this week that it was ready to quickly raise its crude exports to pre-sanctions levels once a deal is signed.

Iranian international relations analyst Fayaz Zahed said the government needed to be very careful about Moscow's possibly shifting interests.

"Now that Russia is under sanctions, it is perhaps no longer interested in resolving the Iran nuclear issue, a position that could be very damaging," he said.

The coming days are seen as pivotal because of the rate at which Iran is making nuclear advances.

Its stockpile of enriched uranium has now reached more than 15 times the limit set out in the 2015 accord, the IAEA said this week.