Experts from Iran and six world powers have resumed talks in Geneva on how to implement a landmark nuclear deal.
Under last month's interim agreement, Iran will curb its disputed nuclear program in exchange for some easing of international sanctions.
On December 12, Iran broke off the talks in protest against the blacklisting by Washington of a further 19 companies and individuals under existing sanctions.
Tehran said the move was against the spirit of the interim deal.
Despite the Iranian action, progress was reported during the December 9-12 meeting in Vienna.
The six powers -- the United States, Russia, China, Britain, France, and Germany -- are seeking to scale back Iran's nuclear program to prevent it from developing nuclear weapons.
Tehran denies any such intention.
Based on reporting by Reuters and ITAR-TASS