The European Union says Iranian and international technical experts have exchanged details on proposals to end the standoff over Tehran's nuclear program.
A statement said talks in Istanbul lasted a full day and ended early Wednesday.
The technical talks followed three rounds of negotiations between Iran and six world powers that have failed to produce a breakthrough,
The statement said the experts explored positions on a number of technical subjects.
The talks will be followed by a meeting between Iran's No. 2 nuclear negotiator Ali Bagheri and Helga Schmid, the EU official in charge of the talks.
No date for the meeting was announced.
The EU, U.S. and other nations suspect Iran's nuclear program is aimed at developing atomic weapons. Iran denies this, and says it is for peaceful purposes.
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