She spoke after a meeting Thursday in Brussels with the foreign ministers of Britain, France, Germany and Iran to discuss the 2015 agreement, which limited Iran's nuclear program amid concerns it was working to develop nuclear weapons, and in exchange gave Iran relief from financial sanctions.
Iran has insisted its nuclear program was solely peaceful in nature. Iranian Foreign Minister Mohammad Javad Zarif did not appear alongside the other diplomats as they spoke to reporters, but on Wednesday expressed support for the agreement while accusing the United States of implementing destructive policies.
Mogherini said the deal has allowed for deeper cooperation and dialogue with Iran on all issues as she stressed the need to see its continued success.
'The unity of the international community is essential to preserve a deal that is working, that is making the world safer, and that is preventing potential nuclear arms deal in the region, and we expect all parties to continue to fully implement this agreement,' she said.
French Foreign Minister Jean-Yves Le Drian said all parties must respect the nuclear deal, including the United States, which was part of the group that included Britain, China, France, Russia and Germany to negotiate the agreement.
British Foreign Secretary Boris Johnson said it is important to build 'worldwide support' for the deal and give Iran the chance to show it is a 'good neighbor in the region.'
'It is legitimate and right that we should in parallel - not connected with the JCPOA - but in parallel we should focus on what Iran can do to resolve the appalling crisis in Yemen, to help push forward a peace in Syria and to help resolve other questions in the region,' Johnson said.
He added that he does not think anyone has come up with a better alternative to the Iranian nuclear deal.
Trump on sanctions
U.S. President Donald Trump is expected to decide Friday whether to continue waiving U.S. sanctions that were originally imposed to pressure Iran to give up any nuclear weapons work.
Trump has been a harsh critic of the JCPOA, saying Iran got too much of a benefit while giving up too little.
The agreement was put in place through a United Nations Security Council resolution with monitoring by the International Atomic Energy Agency, which has certified that Iran is complying with its responsibilities that include limiting its enrichment of uranium and dismantling equipment.