The three European parties to the deal -- Germany, France and Britain -- will meet in Paris on Monday to discuss how to respond to Iran stepping back from its commitments under the accord, Maas said.

Tehran last week resumed enrichment at the underground Fordow plant south of Tehran in the latest in a series of moves away from the agreement, taken since Washington's withdrawal in May last year and reimposition of sanctions.

"We are very concerned to see that there are other uranium enrichments that Iran has not only announced, but is also carrying out," Maas said as he arrived for talks with fellow EU foreign ministers in Brussels.

"We want to preserve the JCPOA but Iran will have to return to his obligations and comply with them. Otherwise we will reserve for ourselves all the mechanisms laid down in the agreement."

The accord, formally known as the Joint Comprehensive Plan of Action or JCPOA, includes a dispute resolution mechanism that goes through various stages with numerous deadlines.

After a process probably lasting several months, it can eventually culminate in the UN Security Council voting on whether Iran should still have relief from sanctions lifted under the deal.

Britain, China, France, Germany and Russia have been trying to salvage the hard-won agreement and say Iran's phased suspension of its obligations under the deal since May makes that more difficult.