A prominent American anchor on Iranian state television’s English-language service has been arrested in the US on undisclosed charges, according to her employers at the state-backed TV channel Press TV.

Marzieh Hashemi, born Melanie Franklin of New Orleans, appears on the English-language news channel backed by the Iranian government which regularly promotes the worldview of the Middle Eastern state to an international audience.

Iran’s foreign minister, Javad Zarif, criticised the arrest, which comes at a time of heightened tensions with the US – and as Iran faces increasing criticism over its own arrests of dual nationals.

“The arrest of Marzieh Hashemi by America is an unacceptable political act that tramples on freedom of speech,” Zarif told state run Al-Alam TV.

“The Americans must immediately end this political game,” he said.

Press TV said Hashemi was arrested at St Louis airport on Sunday and transferred by FBI agents to a detention centre in Washington DC, where she was held for two days before managing to contact her family.

Press TV claimed that she has yet to be charged or informed of the reason for her detention, saying that Hashemi was made to remove her hijab and expose her forearms for a photograph. The channel also claimed she has been denied halal food and was instead offered pork products to eat, leaving her malnourished.

The FBI declined to comment and it is not possible to independently verify the claims made by Press TV.

“Her relatives were unable to contact her, and she was allowed to contact her daughter only two days after her arrest,” the channel said in a statement.

“Press TV would like to hereby express its strong protest at the recent apprehension and violent treatment of Ms Marzieh Hashemi, born Melanie Franklin in the United States, who is currently serving as an anchor for the English-language television news network.”

Hashemi converted to Islam and moved to Iran after being inspired by the Iranian revolution. She was reportedly visiting family members back in the US when the arrest was made.

Press TV broke into its planned broadcasting to cover the arrest and has published more than a dozen statements of support on its website, including from Lauren Booth – the sister-in-law of Tony Blair – who describes Hashemi as a “personal friend”.

The channel, whose presenters have included George Galloway and Jeremy Corbyn, lost its licence to broadcast on television in the UK in 2012 after being found guilty of breaches of the Ofcom code. The channel had previously been fined £100,000 for broadcasting an interview conducted under duress with an imprisoned journalist.

Corbyn earned £20,000 ($25,698) for various appearances on Press TV over several years, including a brief stint hosting a phone-in on the channel.

However, the channel continues to be active on social media, earning attention when it covered an attempt to deselect the Labour MP Joan Ryan, who is chair of Labour Friends of Israel.

Last week, Iran confirmed it is holding US navy veteran Michael R White at a prison in the country, making him the first American known to be detained under Donald Trump’s administration.

Nazanin Zaghari-Ratcliffe, a British-Iranian woman, has been held in Tehran since April 2016. She recently started a hunger strike in protest against being denied access to medical care.

An Iranian foreign ministry spokesman, Bahram Ghasemi, told state TV that Hashemi’s arrest indicates the “apartheid and racist policy” of the Trump administration.

“We hope that the innocent person will be released without any condition,” Ghasemi said.