US Defense Secretary Mark Esper said Saturday he was "not surprised" Iran had turned on advanced centrifuges to increase uranium stockpiles, a further breach of the 2015 nuclear deal which Washington pulled out of last year.

"I'm not surprised that Iran has announced that it's going to violate the JCPOA," Esper said in Paris.

"It's no surprise that the Iranians are going to pursue what the Iranians have always intended to pursue," he added.