PARIS (Dispatches) -- France lamented on Tuesday a U.S. decision to end a sanctions waiver related to Iran's Fordow nuclear facility.
"We regret the decision of the United States, following Iran's resumption of enrichment on the Fordow site, to terminate an exemption that would facilitate the conduct of civilian projects on this site," foreign ministry spokeswoman Agnes von der Muhll told reporters in an online briefing.
Russia’s foreign ministry said Washington’s move to restore sanctions against Fordow was a breach of international obligations.
"Such decisions are another example of a flagrant violation of international obligations by the United States and its irresponsible attitude towards the agreements being signed and the decisions of the UN Security Council that it not only feels free to openly violate but also tries to impede the process of implementation by all other countries,” it said.
The ministry also stressed that Moscow would continue close cooperation with Tehran on the Fordow reconfiguration.
The Trump administration, which last year pulled out of the Iran nuclear deal and reimposed sanctions on Tehran, had until Monday let the work go forward at the Fordow fuel enrichment plant by issuing waivers to sanctions that bar non-U.S. firms from dealing with the Atomic Energy Organization of Iran (AEOI).
Tehran has already scaled down some of its commitments and has threatened to go further if the Western European signatories to the deal -- France, Germany, and Britain -- do not offer economic relief.
The UN atomic agency and Iran itself said this month Tehran is again enriching uranium at the underground site. On Monday, the International Atomic Energy Agency (IAEA) said Iran had informed it that the country had gone beyond another limit of its nuclear deal with major powers by accumulating more than 130 tonnes of heavy water.
"On 17 November 2019, the Agency verified that the Heavy Water Production Plant (HWPP) was in operation and that Iran’s stock of heavy water was 131.5 metric tonnes,” the IAEA said in a report. 
Von der Muhll accused Iran of non-compliance with its nuclear obligations, saying it "may have serious consequences for proliferation".
"Iran's resumption of enrichment activities at the Fordow site, with potentially serious proliferation consequences, is a new step that marks a regrettable acceleration of Iran's withdrawal from the Vienna agreement," he claimed.
Tehran recently resumed low-grade uranium enrichment at its underground Fordow nuclear plant. The country says its reciprocal measures do not violate the nuclear accord and are based on Articles 26 and 36 of the agreement itself, which detail mechanisms to deal with non-compliance.
"France calls on Iran to comply fully with the agreement without delay," von der Muhll said, adding that Paris was continuing its efforts to defuse tensions.
French officials have in recent weeks stepped up efforts to try to bring Tehran and Washington back to the negotiating table, but with little sign of success.
They are trying to convince Iran to go back on a raft of decisions in response to the Europeans’ failure to protect the country from the U.S. sanctions.