A Downing St spokesperson said:
The Prime Minister had a brief conversation with Iranian Foreign Minister Mohammed Javad Zarif in the margins of the Supporting Syria conference in London today.
The Prime Minister and Foreign Minister Zarif agreed that progress had been made on the bilateral relationship, and there was an opportunity to do more to boost trade links.
The Prime Minister raised concerns over the dual UK-Iran nationals held in Iranian prisons, pressing for swift progress in their cases.