Talks in Istanbul between world powers and Iran over Tehran's controversial nuclear program ended Saturday with a commitment to meet again in the Iraqi capital, Baghdad, May 23.

After nearly 10 hours of talks, both sides said the meeting was held in a “positive and constructive” atmosphere.

European Union foreign policy chief Catherine Ashton described the discussions as “constructive” and “useful,” adding the meeting in Baghdad would be part of a “step-by-step” approach. U.S. Deputy National Security Adviser for Strategic Communications, Ben Rhodes, called the talks a “positive first step.” He said the agreement for the meeting in May is an additional positive sign.

Iran's chief negotiator, Saeed Jalili, said Saturday's talks “saw important common ground being developed.” He said that “various issues for cooperation and issues for talks were agreed upon for the next meeting.”

But apart from both sides recognizing the importance of abiding by the Nuclear Non-Proliferation Treaty, and acknowledging Tehran's right to develop nuclear energy, there were no other details of what common ground was achieved.

Saturday's talks between diplomats from Iran and the five permanent members of the United Nations Security Council plus Germany were the first since a previous round of talks collapsed 15 months ago, also in Istanbul, amid mutual recriminations.

A VOA correspondent in Turkey said Iran also held bilateral talks with China, Russia and Turkey, but turned down a meeting with the United States. He added that, despite that snub, some Western powers believe Iran has shown more of a willingness to discuss nuclear issues than it did at last year's talks.

“They are saying that Iranians are sort of engaging with them and this is what we didn't have back in 2011 when they first met in Istanbul.”

Saturday's meetings came at a time of increased international pressure on Tehran. New U.S. and European Union economic sanctions against Iran are due to go into effect July 1, while Israel has warned it may take military action. U.S. President Barack Obama has also warned the latest diplomatic efforts are the last chance for diplomacy to work.

Observers say next month's meeting in Baghdad will be a key test of those efforts, as the talks are expected to start focusing on concrete measures to allay international concern over Iran's nuclear program.