Iran emphasized its right to continue to enrich uranium during crucial talks with world powers in Baghdad aimed at resolving Western concerns over its nuclear program, Iranian chief negotiator Saeed Jalili said on Thursday.

In a televised news conference after the close of the talks, Jalili said that a peaceful nuclear project was "an undeniable right of the Iranian nation ... especially the right to enrich uranium."

The negotiator said Iran had abided by its obligations under the nuclear Non-Proliferation Treaty and it insisted on establishing a complete fuel cycle.

Jalili denied the P5+1 countries, the United States, Russia, China, France, Britain and Germany, had offered a new package of proposals during the meeting: "They proposed one suggestion about the issue of uranium."

Iran's insistence that world powers acknowledge what it sees as its right to enrich uranium emerged as a significant difference a senior U.S. administration official said.

"Obviously [that] was not something we were prepared to do," the official said, echoing the U.S. view that Iran does not automatically have this right under international law because, it argues, Iran is in violation of its obligations under counter-proliferation safeguards.

"These were difficult talks ... obviously we were far apart [at the start]," said the official, who declined to be identified due to the sensitivity of the subject.

During the next round of talks, set for Moscow on June 18-19, the six world powers will continue to work toward a deal for a suspension of enrichment of uranium to a fissile purity of 20 percent, the official said.

That is the nuclear advance most worrying to the West since it clears technical obstacles to reaching 90 percent, or bomb-grade, enrichment. Iran says it will not exceed 20 percent and the material will be made into fuel for a research reactor.

"We never expected to get that agreement [on 20 percent] here in Baghdad," the official said. "There is agreement to address all aspects of 20 percent as we put it on the table."

The official said the six powers were going to try to advance the talks "as fast as we can". But it was too early to talk about technical level or expert meetings because the political issues still needed to be clarified.

He added, however, that looming additional sanctions were likely to raise pressure on Iran to seek an agreement ahead of a further round of talks in mid-June. "Maximum pressure is not yet being felt by Iran," the official said, adding there were many other potential sanctions that remained to be employed.

Straight after the talks, the head of the U.S. negotiating team, Wendy Sherman, was headed to Israel, where she is due to meet with Prime Minister Benjamin Netanyahu and his advisers on Friday. Sherman will update Israeli officials on the talks in Baghdad, and on preparations for the third round of talks in Moscow in June.

The United States and its allies suspect Tehran is trying to develop a nuclear weapons capability and have imposed tough sanctions on Iran's energy and financial sectors to try to force it to compromise and open up its activities to scrutiny.

Iran has long stated that its activities are purely peaceful however, and pushed for an overt acceptance of its right to enrich uranium and an easing of sanctions, diplomats said.

Tehran wants any nuclear deal to spare it from an EU embargo on its oil exports to be phased in fully by July 1. It also wants an end to trade and diplomatic sanctions imposed since 2006.