Iran's foreign minister is under attack from hardliners after reportedly shaking hands with the US president at the UN in New York.
There has been no official confirmation that the handshake between Mohammad Javad Zarif and Barack Obama took place but domestic media have quoted "informed" sources as saying it happened by accident on the sidelines of the UN General Assembly this week.
The encounter comes amid fierce debate in Tehran over the future of relations with Washington in the wake of Iran's nuclear agreement with world powers. Ayatollah Ali Khamenei has made clear that the deal will not change Iran's hostile relations with the US, which has been interpreted by hardliners as suggesting that any Iranian official who met the US president would be crossing a "red line".
The ayatollah's stance is designed, in part, to appease his hardline support base, which felt undermined by the compromises made during the nuclear negotiations. He also suspects the US of pursuing a policy of regime change in Iran since the 1979 Islamic revolution.
Division over the future of ties with the US centre on concerns among regime conservatives that moderate politicians are trying to ease tensions with Washington through co-operation over the conflict in Syria.
Hamid-Reza Taraghi, a conservative politician, said on Monday that the "unjustifiable" handshake was "probably accidental" but that parliament would determine whether Mr Zarif's gesture was deliberate or part of a "conspiracy". If deliberate, Mr Zarif would "definitely face impeachment".
More from the Financial Times:
"We don't think [Mr Zarif] could dare to act contrary to the orders of the supreme leader," Mr Taraghi said.
Mansour Haghighatpour, another political conservative and member of the parliament's national security and foreign policy committee, said parliament would not remain indifferent should it be confirmed that Mr Zarif had ignored the regime's red lines.
"There should not be talk of any handshakes with US officials as long as the US supports terrorists and does not respect our nation's rights," Mr Haghighatpour told Tasnim, a news agency close to the Revolutionary Guards.
Whether the threats of impeachment would be acted on remains unclear. Mr Zarif is seen by many Iranians as a national hero who spearheaded nuclear talks with the world's major powers to achieve a breakthrough deal that would lift crippling economic sanctions.
In a recent television interview in the US, Hassan Rouhani, the centrist president, said that despite "the distance, the disagreements, the lack of trust" between Tehran and Washington, both countries were moving towards decreasing the enmity between them. He also indicated in the US the possibility of co-operation with Washington over regional issues.
"The handshake has symbolic importance in line with what has happened during the nuclear talks to extend co-operation from nuclear matters to regional issues," said a reform-minded analyst. "The issue of the US is linked to domestic politics."