Diplomatic sources close to the International Atomic Energy Agency (IAEA) said the Turkish envoy, Hakan Fidan and U.S. Ambassador Glyn Davies had exchanged views over Iran's nuclear program.
The Turkish envoy met also with Iran's envoy, Ali Asghar Soltanieh, and IAEA chief Mohamed el Baradei earlier in the day.
On a question whether Tehran would agree to store part of its low-enriched uranium in Turkey, Fidan told the Anadolu Agency that Iran had demanded that it could exchange its low-enriched uranium with a higher enriched material, but only on its own soil, an offer which sources have said was unlikely to receive a positive response from the six nations.
Turkey's energy minister said earlier this month that it could store enriched uranium from Iran in response to a UN suggestion that Tehran send its low-grade enriched uranium to a third country.
Iran insists that its nuclear program is peaceful and aimed at generating electricity. But there are concerns in the West that Tehran's nuclear ambitions have military dimensions to it.