A prominent American-born Iranian journalist who was held in the US as a witness has been released from jail, according to an advocacy lawyer.

Marzieh Hashemi was freed in Washington DC after being detained for 10 days, an attorney with the American-Arab Anti-Discrimination Committee told the BBC.

Ms Hashemi, who works for Iran's state broadcaster Press TV, was taken into custody in St Louis earlier this month.

Her detention came after Iran arrested four Americans.

Abed Ayoub, a lawyer with the American-Arab Anti-Discrimination Committee, told the BBC she was now with her family in Washington DC.

Why was she arrested?
The 59-year-old producer and presenter was detained on 13 January after arriving in St Louis, where she was working on a documentary about Black Lives Matter, her son told the Associated Press news agency.

A court order unsealed on Friday confirmed that Ms Hashemi, referred to by her birth name of Melanie Franklin, was being held as a material witness in a criminal case, pending her testimony, and was not charged with a crime.

Authorities can hold material witnesses if they can prove their testimony is critical to a criminal case and if they are deemed a flight risk.

Iranian Foreign Ministry spokesman Bahram Qasemi condemned the treatment of Ms Hashemi.

Her employer, the English-language state broadcaster Press TV, issued a statement expressing "strong protest".

According to the outlet, Ms Hashemi told her family by phone on Tuesday that she had been "subjected to violent and abusive treatment from the very onset".

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.

Why are relations so poor?
Tensions have been high between the US and Iran under President Donald Trump. In 2018 he pulled the US out of an international nuclear deal with Iran and reimposed sanctions.

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.

Earlier this month, Iran confirmed the arrest of an ex-US sailor, Michael White. It is unclear what charges he faces.

The Trump administration was open to discussing prisoners last year, but Iranian officials refused, CBS News reports.

The US and Iran do not maintain diplomatic relations, and communications between the two nations are passed along by Swiss diplomats.