World powers and Iran have formally announced a comprehensive nuclear accord.

Federica Mogherini, the European Union’s foreign policy chief, said: “Today is an historic day.”

She added that it was a great honour “for us to announce that we have reached an agreement on the Iranian nuclear issue”.

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Ms Mogherini appeared on stage in Vienna alongside Iranian foreign minister Mohammad Javad Zarif.

She said: “We are creating the conditions for building trust.

“No-one ever thought it would be easy. … Despite twists and turns in the talks, hope and determination enabled us to overcome all the difficult moments.”

She said the deal involves Iran “under no circumstances” obtaining or building nuclear weapons.

US president Barack Obama said every path to a nuclear weapon will be cut off for Iran following the historic agreement.

Mr Obama spoke from the White House immediately after the official announcement of the deal.

Addressing sceptics of the agreement, Mr Obama said: “This deal is not built on trust. It is built on verification.”

He insisted that the accord ensures that Iran “will not develop a nuclear weapon”.

The US leader added that Iran‘s compliance will be verified by inspections.