By CNN's Ivan Watson in Istanbul

Iran and six world powers held "constructive and useful" talks Saturday in Turkey as international diplomats seek to persuade Tehran to rein in its nuclear program.

"We have agreed that the nonproliferation treaty forms a key basis for what must be serious engagement to ensure all the obligations under the treaty are met by Iran while fully respecting Iran's right for the peaceful use of nuclear energy," EU foreign policy chief Catherine Ashton said following the meeting with Iran's top negotiator, Saeed Jalili, in Istanbul.

Jalili had said ahead of the talks that he intended to bring "new initiatives" to the table.

Ashton said Saturday's meeting was a basis to establish a "sustained process of serious dialogue."



The next meeting between Jalili and delegates from the five permanent members of the United Nations Security Council - the United States, France, Russia, China, and Britain - and Germany, will be held May 23 in Baghdad. Experts in the nuclear field will meet ahead of next month's meeting.

"We expect subsequent meetings will lead to concrete steps towards a comprehensive negotiated solution which restores international confidence in the exclusively peaceful nature of the Iranian nuclear program," Ashton said.

The group of delegates - also known as the P5+1 - has spearheaded diplomatic efforts to persuade Iran to limit its nuclear program, which Iran has said is purely peaceful. U.N. and Western leaders suspect it of having military aims, including a possible nuclear weapon.

Jalili had dinner Friday night with Ashton, who is leading the international negotiating team.

Ashton said the atmosphere with Jalili was good, going into the talks, but that "much depends on what Iran is putting on the table today."

Iran last met with the six powers for talks on its nuclear program 15 months ago. That meeting, also in Istanbul, was widely regarded as ending in failure when Iran presented what the international side said were preconditions for talks.

Going into Saturday's meeting, the indications from behind the scenes were that both sides want to make progress.

Iranian Foreign Minister Ali Akbar Salehi said in an opinion piece published Friday in the Washington Post that Tehran is committed to a peaceful program, but it needs to see trust from the international side.

"Despite sanctions, threats of war, assassinations of several of our scientists and other forms of terrorism, we have chosen to remain committed to dialogue," he wrote.

"In the upcoming talks, we hope that all sides will return to the negotiating table as equals with mutual respect; that all sides will be committed to comprehensive, long-term dialogue aimed at resolving all parties' outstanding concerns; and, most important, that all sides make genuine efforts to reestablish confidence and trust."

However, Iran's official Press TV cited a source close to the Iranian delegation in reporting Friday that Iran sees little encouragement coming from the remarks of European and U.S. officials ahead of the talks.

Iran has been under increasing pressure to accept international demands to restrict its nuclear program, including a series of harsh economic sanctions imposed by European nations and the United States.

Last month, Iranian officials signaled they were ready to engage with the International Atomic Energy Agency, the U.N. nuclear watchdog, over the issue.

Iran suggested last week that one proposal may be a reduction in the amount of uranium it enriches to 20%, but it was unclear if such a proposal was still on the table.

While the enrichment isn't enough to create nuclear weapons, which require a uranium content of 90% or more, analysts and inspectors say it is step toward being able to create a nuclear weapon.

Last month, the IAEA noted what it called a sharp and troubling increase in Iran's uranium enrichment capabilities.

Iran says the enrichment is for research and medical needs.

As a signatory to the Nuclear Nonproliferation Treaty, Iran has the right, like other countries, to enrich uranium for commercial and research reactors. But the same facilities that are used for peaceful enrichment can be used to enrich uranium for a bomb, and inspectors say they have not been able to fully gauge Iran's intentions.

CNN's Bharati Naik contributed to this report.