"There will need to be decisions made in places like Tehran and Moscow," State Department spokesman Ned Price told reporters after the European Union announced a pause in negotiations on the deal limiting Iran's nuclear program.

"We are confident that we can achieve mutual return to compliance with the JCPOA if... those decisions are made in places like Tehran and Moscow," Price said, using the acronym for the deal formally known as the Joint Comprehensive Plan of Action.

The current round of talks between world powers and Iran, taking place in the Austrian capital Vienna, had appeared close to its goal until Russia made a sudden new set of demands last week.

Russia said it wanted guarantees that the Western economic sanctions imposed in retaliation for its invasion of Ukraine would not affect its trade with Iran.

Price told reporters that "the new Russia-related sanctions are wholly and entirely unrelated to the JCPOA" and "shouldn't have any impact" on the talks.

"We have no intention of offering Russia anything new or specific as it relates to these sanctions," he added.

Price confirmed that the US negotiator, Rob Malley, had returned to Washington with his team for the time being.

Price warned that "there is very little time remaining" to save the accord, which began unravelling when former US president Donald Trump withdrew the United States in 2018.