A Western diplomat, speaking on condition of anonymity, says Iran has yet to give a "clear and concrete response" to a proposal from world powers for resolving the decade-long dispute over Iran's nuclear program.
The statement came as Iran and six world powers -- the United States, Russia, China, Britain, France, and Germany -- began a fresh round of talks in Almaty, Kazakhstan, on April 5.
Iran’s deputy nuclear negotiator Ali Bargheri said his delegation responded to all matters put to them.
"Representatives of the six countries tabled their questions and their own proposals and responses to the proposals tabled earlier by the Islamic Republic of Iran," he said, "and [Iran's chief nuclear negotiator Said Jalili] answered all their questions."
Bargheri said talks on the sidelines would continue before all the representatives reassembled for another meeting.
"A number of bilateral meetings took place between the representatives of the Islamic Republic of Iran and representatives from some of the participating countries," he said. "Tonight, we expect to have more bilateral meetings and tomorrow, Saturday, we will have a plenary meeting with the 5+1 representatives."
It is the fifth round of nuclear talks in two years. The meeting in Kazakhstan’s commercial capital is a follow-up to a session the parties held at the end of February in Almaty.
Expectations for any breakthrough were low coming into this latest meeting, with some saying it was unlikely there would be any progress until after Iran’s June presidential election.
At a February meeting in Almaty, world powers offered to ease some economic sanctions if Tehran agreed to suspend production of higher-grade uranium, which could be used to make weapons.
Iran denies any intentions to make nuclear weapons and insists its nuclear program is for civilian use only.
With reporting by RFE/RL's Rikard Jozwiak in Brussels, AFP, and Interfax