The UN atomic energy watchdog chief said Tuesday that he was “extremely concerned” about Iran’s lack of cooperation as the EU seeks to unblock talks to revive the 2015 nuclear deal. Talks between world powers and Iran have stalled since mid-March as negotiators seek to return to the landmark accord that curtailed the Islamic republic’s nuclear programme in exchange for sanctions relief. EU diplomat Enrique Mora, who chairs the negotiations, will visit Tehran this week, Iran announced Monday, as the United States — which is seeking to come back to the deal it unilaterally left in 2018 — voice…