France's foreign ministry has confirmed two of its citizens are being detained in Iran and has demanded their release, reports BBC News.
"The French government condemns these baseless arrests," a statement said.
It did not identify the pair, but the head of a French education union said an employee and her husband had gone missing while on holiday in Iran.
On Wednesday, the Iranian intelligence ministry said two Europeans had been arrested for planning to cause "chaos, social disorder and instability".
The ministry said they shared the same nationality and alleged that they were "agents" sent to Iran to "take advantage" of protests by teachers and other workers, without providing evidence.
Earlier this month, scores of teachers took to the streets in more than dozen Iranian cities to demand fair wages, better conditions, and the release of colleagues detained ahead of the protests.
France said its ambassador in Tehran was seeking consular access to its citizens and would remain "fully mobilised" until they were released.
Christophe Lalande, federal secretary of France's FNEC FP-FO education union, told Reuters news agency that there was a "strong presumption" that one of its staff and her husband were the two arrested.
The BBC understands that the union official is named Cécile Kohler.
Iranian authorities are believed to have arrested dozens of Western citizens - most of them Iranians with dual nationality - in recent years. Human rights activists have accused the Islamic Republic of using them as bargaining chips in negotiations with the West.