VIENNA - Iran and six world major countries have adopted an agreement on the Iranian nuclear issue, European Union (EU) foreign policy chief Federica Mogherini formally announced here on Tuesday.

"What we are announcing today is not just a deal, it is a good deal ... today is a historical day," Mogherini told a joint press conference with Iranian Foreign Minister Mohammad Javad Zarif.

Ensuring "Iran's nuclear program will be exclusively peaceful," the two diplomats said "Iran confirms that Iran under no circumstances will seek or acquire nuclear weapons."

The nuclear deal reached with the six world major countries will help build confidence, Zarif said.

"The deal will help building confidence between Iran and the powers," Zarif said.

Earlier on Tuesday, a diplomatic source confirmed that the historic agreement had been reached between Iran and the six world major countries.

The comprehensive agreement was clinched between Iran and the P5+1 group, namely Britain, China, France, Russia and the United States plus Germany, after more than two weeks of tough bargain in the capital city of Austria.(Xinhua)