European Union's foreign policy chief Josep Borrell said on Friday that the way has been paved to resume negotiations for a nuclear deal with Iran after a two-month deadlock.

Borrell said a mission by EU envoy Enrique Mora this week to help revive the 2015 nuclear pact between Iran and world powers had gone "better than expected".

Speaking on the sidelines of the G7 foreign ministers meeting in Germany, Borrell said, "These things cannot be resolved overnight. Let's say the negotiations were blocked and they have been de-blocked", with the prospect of "reaching a final agreement".

The broad outline of the deal that aims to revive the accord which restrains Iran's nuclear programme in return for relief from economic sanctions was essentially agreed in March.

Negotiations have been on hold since March, primarily over Tehran's insistence that the United States remove the Islamic Revolutionary Guard Corps from its list of foreign terrorist organizations.

Speaking as talks coordinator Enrique Mora arrived back in Europe, Josep Borrell said Iran's response had been "positive enough" after Mora had delivered a message that things could not continue as they were.

According to a Reuters report, another senior EU official sounded a more cautious tone.

"We still have difficult obstacles on the way for an agreement," he told reporters, adding that at least Iran and the U.S. remained engaged.

Mora has been in Tehran this week in what has been described as the last chance to salvage the 2015 accord, which then U.S. President Donald Trump withdrew from in 2018. Britain, China, France, Germany and Russia are also parties to the accord.

In a bizarre incident, Mora and his team were held at Frankfurt airport for several hours on return from the Iranian capital on Friday.

"We were kept separated. Refusal to give any explanation for what seems a violation of the Vienna Convention," he said on Twitter.

Iran has blamed Israel for having played a role in the incident.