Iran faces international pressure in two separate meetings over its nuclear program on May 15.
In Vienna, the International Atomic Energy Agency once again urged Iran to stop blocking its investigation into suspected atomic bomb research by Tehran.
IAEA Deputy Director Herman Nackaerts told reporters there was determination "to solve these issues."
Later on May 15 in Istanbul, the European Union's top diplomat will meet Iran's chief nuclear negotiator Said Jalili.
The Istanbul meeting between Jalili and EU foreign policy chief Catherine Ashton, who represents six world powers, follows a failed round of big power diplomacy in Kazakhstan in early April.
The six world powers are the United States, Russia, China, France, Britain, and Germany.
Western powers accuse Iran of using its nuclear program to seek a weapons capability, a charge Iran denies.
Based on reporting by Reuters and AFP