President Barack Obama and Iran's foreign minister Mohammad Javad Zarif shook hands during a brief exchange at the U.N. General Assembly in New York.
Monday's encounter was the first between a sitting American president and a top Iranian diplomat since the 1979 ouster of a Western-backed monarch in Iran during the Islamic Revolution.
White House press secretary Josh Earnest and Iran's Foreign Ministry Spokesperson Marzieh Afkham confirmed the handshake and a brief conversation took place.
"They exchanged pleasantries," Earnest said.
There has already been some increased contact between the two countries in recent years. Obama and his counterpart Rouhani, spoke by telephone in 2013 and the nuclear talks involved direct talks between Iranian and U.S. foreign ministers.
The handshake could prompt hardliners in Iran to protest and to call on Zarif to provide an explanation. The minister, who is known as a pragmatist, had to appear before parliament for taking a 15-minute walk down Geneva sidewalks with Kerry during nuclear talks in January. A landmark nuclear deal was reached between Tehran and six major global powers in July aimed at curbing the country's nuclear program in exchange for lifting economic sanctions.