The EU's foreign policy chief said Monday there was "no alternative" to the Iran nuclear deal, after U.S. Secretary of State Mike Pompeo vowed unprecedented sanctions against Tehran following Washington's withdrawal from the pact.

"Secretary Pompeo's speech has not demonstrated how walking away from the JCPOA (nuclear deal) has made or will make the region safer from the threat of nuclear proliferation or how it puts us in a better position to influence Iran's conduct in areas outside the scope of JCPOA," Federica Mogherini said in response to an address by Pompeo on Monday.

"There is no alternative to the JCPOA."