The EU's diplomatic chief Josep Borrell on Monday voiced regret at Tehran's latest decision to reduce its commitments to the beleaguered 2015 Iran nuclear deal.

"Deeply regret Iran's latest announcement on #JCPOA. As ever we will rely on @iaeaorg verification," Borrell tweeted, using an abbreviation for the deal's formal name.

"Full implementation of #NuclearDeal by all is now more important than ever, for regional stability & global security. I will continue working with all participants on way forward."