The EU's short statement on the talks between the six powers and Iran offered no clue how the proposals were received by the Iranian experts or whether any progress had been made.
The two sides agreed in February to hold the technical discussions at meeting between officials in the Kazakh city of Almaty, when the United States, China, Russia, Britain, France and Germany offered modest sanctions relief in return for Tehran curbing its most sensitive nuclear work.
Iran says its nuclear programme is peaceful but Western powers suspect Tehran of seeking nuclear weapons capability.
The statement by Michael Mann, a spokesman for EU foreign policy chief Catherine Ashton, reaffirmed that Monday's technical talks would be followed by another meeting at the political level in Almaty on 5-6 April.
Western diplomats have made clear they want to see a substantive response from Iran to the six powers' proposals at the meeting.
In Istanbul, experts from the six powers, led by nuclear expert Stephan Klement, gave Iran further details of the "revised confidence-building proposal" they put forward at an earlier meeting in Almaty, Mann said.
"The meeting also provided an opportunity for both [six-power] and Iranian experts to explore each other's positions on a number of technical subjects," he said, declining to go beyond the statement.
Ashton oversees contacts with Iran on behalf of the six powers.
US President Barack Obama insisted yesterday that "now is the time" for Iran to take meaningful steps to resolve its nuclear standoff with the West as he issued a direct appeal to the Iranian people before his first official trip to Israel.
Obama will hold talks in Israel on Wednesday (20 March) with Prime Minister Benjamin Netanyahu, who repeatedly has called for a "credible" military threat against Iran and hinted at the prospect of a unilateral Israeli attack.
