One day after the invasion of Ukraine began the United States announced that it will continue to work with Russia on reviving the 2015 Iran nuclear agreement.

Washington will continue to engage with Moscow over efforts to prevent Iran from developing nuclear weapons, even though Moscow's invasion of Ukraine had made it a "pariah on the world stage," State Department spokesperson Ned Price said on Friday.

Price said US officials would now only engage with Russia counterparts on issues of "fundamental to our national security interest."

Some have expressed reservations about continuing to involve Russia in high-stakes diplomatic and security issues, while Moscow has up-ended the international security structures by its attack on Ukraine with the declared aim of replacing its elected government and deciding its foreign policy course.

Many in Iran are criticizing their government for having given Russia control over the nuclear talks. Moscow has increasingly acted as a mediator between Tehran and Washington, while critics in Iran say its intentions cannot be trusted.

"The fact that Russia has now invaded Ukraine should not give Iran the green light to develop a nuclear weapon," Price added.

Iran’s chief negotiator left the negotiations just days before the invasion and returned to Tehran ostensibly for consultations.

Another US official was quoted by Reuters as saying that significant progress has been made in the talks but serious issues remain to be resolved.