A spokesman for the European Union's foreign policy chief, Catherine Ashton, said "Iran needs to understand that there is an urgent need to make concrete and tangible progress," The New York Times reported.
Iran denies its nuclear program has any military aims but the five permanent members of the United Nations Security Council along with Germany want Iran to obey U.N. resolutions to suspend uranium enrichment and allow inspections.
Tuesday's session in the town of Almaty ended after approximately two and a half hours with no indication when negotiations would resume.
Western diplomats involved with the talks have expressed skepticism that chief Iranian negotiator Saeed Jalili would be willing to make compromises ahead of his country's June presidential elections.
Iran has continued to increase its stockpile of uranium enriched to 20 percent purity since nuclear talks ended in June.
It has also begun installation of a new generation of centrifuges and has not yet completed an agreement on inspections with the International Atomic Energy Agency.
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