Claims that Britons have been arrested after protests in Tehran are being investigated by the Foreign Office.
Reports on Iranian state television said some British passport-holders had been detained following unrest sparked by the recent election.
A spokesman for the Foreign Office said: "We are aware of the reports and we will be looking into them."
Riot police and protesters clashed in the streets around Iran's parliament on Wednesday night as hundreds of people converged on a Tehran square in defiance of government orders banning demonstrations.
It followed a declaration by the country's supreme leader that the government would not yield to the opposition.
Ayatollah Ali Khamenei accused the US, Britain and other foreign powers of being behind the street protests.
