Signaling increased alarm over Iran’s breaches of the 2015 nuclear agreement, the deal’s European members took a step on Tuesday that could lead to its possible collapse.

In a joint statement, the foreign ministers of France, Germany and Britain, plus the top foreign policy official of the European Union, expressed “deep concern that Iran is pursuing activities inconsistent with its commitments” under the accord, known as the Joint Comprehensive Plan of Action.

The statement by the European members was their strongest response yet to at least two Iranian violations of the agreement in recent days: exceeding the stockpile of uranium it is allowed to keep, and raising the enrichment level of some of that stockpile above the purity required for civilian use.

They exhorted Iran to return to full compliance “without delay” and said that a joint commission for resolving disputes under the accord “should be convened urgently” to address the problem.