Iran and the UN agency agreed in March on an approach to resolve the issue of the nuclear material found at Marivan, Varamin and Turquzabad -- sites that had not been declared by Iran as having hosted nuclear activities.

But in a report on Monday the International Atomic Energy Agency said it still had questions which were "not clarified" despite long-running efforts to get Iran to explain the presence of the nuclear material.

The IAEA board of governors is to hold a meeting on Monday for which Britain, France, Germany and the US have prepared a draft resolution "calling on Iran to cooperate on the question of undeclared sites", according to a European diplomatic source.

"We will respond firmly and appropriately to any unconstructive action at the board of governors," Iranian foreign ministry spokesman Saeed Khatibzadeh said in a statement.

"The responsibility for its consequences falls on the shoulders of those who see the board of governors and the director-general's report as leverage and a tool of political games against Iran," he added.

The issue is one of the remaining obstacles to reviving a 2015 deal that gave Iran relief from sanctions in return for guarantees that the Islamic republic is unable to develop a nuclear weapon -- something it has always denied wanting to do.

The agreement, known formally as the Joint Comprehensive Plan of Action, was torpedoed in 2018 by the administration of then US president Donald Trump, which withdrew unilaterally and imposed sanctions on Iran.

Tehran has condemned the UN watchdog's report as "not fair and balanced", saying it "does not reflect the reality of the negotiations between Iran and the IAEA."

France had called on Iran to respond "promptly" to the IAEA's requests.

"We are consulting closely with our partners on how to respond to this situation at the next board of governors meeting", its foreign ministry said.

Khatibzadeh called on "countries such as France to refrain from taking positions and making interventions that would cause the cooperation to deviate from its proper path."

These statements were aimed at putting "pressure on the Islamic Republic of Iran on the eve of the meetings of the IAEA board of governors," he added.