An American journalist working for Iran's English-language Press TV has been arrested by US authorities on unspecified charges, the state-run broadcaster said on Wednesday.

Marzieh Hashemi, 59, was arrested upon arrival at St Louis Lambert International Airport on Sunday and transferred by the FBI to a detention facility in Washington, DC, Press TV said.

"Her relatives were unable to contact her, and she was allowed to contact her daughter only two days after her arrest," the Iranian broadcaster reported.

"Hashemi [...] has told her daughter that she was handcuffed and shackled and was being treated like a criminal."

Several local jails around Washington that house federal inmates said they did not have her in custody. FBI officials were not immediately available for comment.

Born Melanie Franklin, Hashemi was in the United States to visit family.

The Muslim convert was quoted as saying by the broadcaster she was prevented from observing her Islamic faith and wearing her headscarf. She was also only offered pork as a meal, which is prohibited in Islam.

The only food she has had over the past two days has been a "packet of crackers", Hashemi was quoted as saying by Press TV.

The account of her treatment could not be independently verified.

An Iranian foreign ministry spokesman on Wednesday called for her immediate release.

"We condemn the illegal arrest of Marzieh Hashemi, the reporter and presenter of Press TV, and the inhumane treatment of her in jail in Washington," Bahram Qasemi was quoted as saying by state news agency IRNA.



Piling on pressure

Hashemi's reported arrest comes amid heightened tensions between Iran and the US.

During his recent trip through the Middle East, US Secretary of State Mike Pompeo said the US is "redoubling" its efforts to put pressure on Iran, accusing it of destabilising the region.

Pompeo vowed to "expel every last Iranian boot" from Syria and urged regional rivals to come together to confront Iran.

US President Donald Trump withdrew the US from the landmark 2015 Iran nuclear accord last year and reimposed sanctions on Tehran, even as other partners in the deal - including China, France, Germany, Russia and the United Kingdom - have sought to maintain it.