
The meeting between Richard Holbrooke and Mohammad Mehdi Akhoondzadeh took place on the sidelines of a meeting in The Hague to discuss Afghanistan.
The US has welcomed Iran's presence at the meeting.
Analysts say the easing of tensions between the US and Tehran is due to a new tone set by the Obama White House.
Earlier, Iran gave a guarded welcome to US plans to increase regional co-operation over Afghanistan.