The six world powers - the United States, Russia, China, Germany, France and Britain - met senior Iranian officials for the first time in 15 months for talks aimed at calming deepening tensions over Tehran's nuclear work.
"They met in a constructive atmosphere," said Michael Mann, spokesman for EU foreign policy chief Catherine Ashton, who represents the powers in dealings with Iran. "We had a positive feeling that they did want to engage."
A second session of talks was scheduled later in the day. Diplomats expect Tehran to lay out "new initiatives" to push forward negotiations.