A BBC journalist with dual British-Iranian nationality has been prevented from flying to the US after falling foul of changes to visa rules.
Rana Rahimpour was told by US authorities she could not travel under a visa waiver scheme.
Under new laws, dual citizens from several nationalities must instead apply for a visa at the US embassy.
But Ms Rahimpour said advice from the embassy on whether the rules had been implemented was unclear.
The UK foreign office website says the rules come in on 1 April, while the US State Department website says the authorities have “begun the process of implementing changes” to the waiver scheme.