Iran has called on the US to release one of its journalists who, it says, was illegally arrested by the FBI while making a family visit.
American-born reporter Marzieh Hashemi was reportedly taken into custody upon landing in St Louis on Sunday and subjected to "inhumane" conditions.
Ms Hashemi's reported arrest came after Iran detained at least four Americans, some on espionage charges.
The FBI declined to comment on the situation in an email to the BBC.
Ms Hashemi, 59, is reportedly now in Washington DC following her arrest at St Louis Lambert International Airport.
US media have been unable to verify Ms Hashemi's situation with any local jails.
What do the Iranians say happened?
Iranian Foreign Ministry spokesman Bahram Qasemi said Iran condemned the treatment of Ms Hashemi.
Ms Hashemi's employer, the English-language state broadcaster Press TV, issued a lengthy statement expressing "strong protest" at Ms Hashemi's situation.
According to the outlet, Ms Hashemi told her family in a phone call on Tuesday she had been "subjected to violent and abusive treatment from the very onset".
She said she did not know why she had been detained. The authorities allegedly forced her to remove her hijab and allowed her to wear only a short-sleeved shirt, going against her Muslim beliefs.
The statement says she was also denied halal (adhering to Islamic law) food, "being offered only pork as a meal and not even bread", and as a result ate just a packet of crackers after her apprehension.
"We, further, call for the immediate and unconditional release of Ms Hashemi, and for the US government to apologize to both the journalist and the international media community for her treatment," Press TV said.
Ms Hashemi was born Melanie Franklin in the US and changed her name when converting to Islam. She is reportedly married to an Iranian.
Maryam Azarchehr, a fellow Press TV journalist, said Ms Hashemi had been in the US for two weeks before she was arrested trying to fly to Colorado from Louisiana.
Ms Azarchehr said Ms Hashemi, a grandmother of three who is on medication for heart conditions, had been chained and shackled in detention. The allegation could not be verified independently.
Why are relations so poor?
Tensions have been high between the US and Iran under President Donald Trump.
At least four Americans have been detained in Iran on what the US has called fabricated charges. Some have been convicted and sentenced to lengthy prison terms; another US man has been missing for over a decade.
Last week, Iran confirmed the arrest of an ex-US sailor, Michael White - the first detention under the Trump presidency - though it is unclear what charges he faces.
In 2018, Mr Trump pulled the US out of the 2015 Iran nuclear deal, reimposing sanctions and souring relations between the two nations.
The US and Iran do not maintain diplomatic relations, and communications between the two nations are passed along by Swiss diplomats.