A spokesman for EU foreign policy chief Catherine Ashton says a first round of talks between Iran and six world powers on Tehran's controversial nuclear program was “constructive,” laying the groundwork for future talks.

Michael Mann said Saturday that world powers believed Iran was serious about engaging in substantive talks after the two sides wrapped up their first session in Istanbul on Saturday.

The meeting marks the first direct talks between Iran and the five permanent members of the U.N. Security Council and Germany – the P5 + 1 – in over a year.

News reports say both sides also expressed an interest in bilateral talks.

The meeting comes at a time of increased tensions between Iran and many Western powers over the nature of Tehran's nuclear program. Iran says its nuclear ambitions are peaceful. However, the U.N., EU, and world powers including the United States have imposed successive rounds of sanctions on Iran because of concerns that it is trying to develop nuclear weapons.

Earlier this week, Michael Singh of the Washington Institute for Near East Policy said the talks could produce results, because Iran is facing huge international pressure.

“I hope that these talks will validate the strategy of trying to use pressure in conjunction with diplomacy to get the Iranians to really shift their course, to change their approach to this nuclear question.”

Members of the P5 + 1 group are the U.S., France, Britain, Russia, China and Germany.