The EU may activate the formal dispute mechanism of the Iran nuclear deal if Tehran does not return to full compliance with it, Germany’s foreign minister warned on Monday.

Speaking to reporters in Brussels ahead of an EU foreign ministers meeting, Heiko Maas said Europeans are “gravely concerned” over Iran’s recent move to start enriching uranium at an underground facility.

“We want to preserve the deal, but Iran must finally return to compliance with the agreement, otherwise we reserve the right to use all mechanisms that are set out in the agreement,” he stressed.

Read more: EU may pull dispute trigger on Iran nuke deal: Germany