Iran's new President is expected to meet the US Secretary of State in Switzerland this week, in what would be the most high level face-to-face talks between the two countries in three decades.
The prospect of an encounter between Hassan Rouhani and John Kerry came after the Iranian President used a speech at the World Economic Forum in Davos to announce a new policy of "constructive engagement" with the outside world.
Diplomats said a meeting with Kerry, who flew into the Swiss town yesterday, was "likely", although not confirmed. It would be a further step in Rouhani's efforts towards restoring relations with the US, which were broken off in 1980.
Rouhani has already spoken directly to President Barack Obama by phone, but diplomatic sensitivities have restricted face-to-face meetings at higher levels.
In September, both presidents declined the opportunity to shake hands at the United Nations General Assembly meeting in New York, despite speculation that they might do so. Ongoing talks between the two countries led to last November's historic deal to end Iran's disputed nuclear programme.