An American newscaster for the Iranian government’s Press TV was released late Wednesday after her 10-day-long detention in federal custody provoked outrage in the US and Iran.

FBI agents arrested Marzieh Hashemi, a US citizen, at St Louis airport on 13 January. She was held as a material witness in an unspecified criminal proceeding, according to documents unsealed by the Department of Justice on Friday. Her detention prompted concerns about the potential first amendment issues of detaining a journalist, as well as religious liberty issues as Hashemi, a practicing Muslim, was reportedly denied Halal food and had her hijab forcibly removed.

“Marzieh and her family will not allow this to be swept under the carpet,” the woman’s family said in a statement shortly after her release. They “still have serious grievances [and] they want assurances that this won’t happen to any Muslim – or any other person – ever again”.

Hashemi has not been charged with any crime and appeared before a federal grand jury at least three times. US law allows the government to arrest and hold so-called “material witnesses” if a judge agrees that the individual has information that is important to a criminal proceeding and may flee if simply subpoenaed to appear in court.

The justice department did not return a Guardian query about the nature of the criminal proceeding or why it took the step of detaining Hashemi to secure her testimony. It may have been due to the fact that she frequently travels to and lives part-time in Iran.

Her release follows intense outrage in Tehran, where journalists gathered earlier on Wednesday to call the detention “illegal” and a “violation of human rights”.

“This shows, for sure, to be a flagrant violation of human rights, a violation of domestic rights, a violation of freedom of speech and the freedom of the press. There is no doubt about that,” said Seyed Mostafa Khoshcheshm, a political analyst in Tehran, according to the Tasnim news agency. The comments came alongside a joint statement from three major Iranian journalist associations condemning the detention.

Supporters of Marzieh Hashemi demonstrate in Washington. Photograph: Cliff Owen/AP

Hashemi’s arrest added fuel to an increasingly tumultuous diplomatic relationship between the US and Iran, which has been unsettled by the Trump administration’s decision to back out of the nuclear deal negotiated by the Obama administration and to reinstitute harsh sanctions.

“The US govt needs to explain how Marzieh Hashemi – a journalist and grandmother – is such a flight risk that she must be incarcerated until she finishes her testimony to a grand jury,” said the Iranian foreign minister, Mohammad Javad Zarif, in a tweet on Monday, which was observed as Martin Luther King Jr Day in the US. “50 years after MLK assassination, US still violates the civil rights of black men and women,” he continued.

Hashemi was born Melanie Franklin in Louisiana and changed her name when she converted to Islam after the Iranian revolution. According to Press TV, she has primarily lived in Iran for over a decade and was in the US to visit a sick family member. Hashemi was also working on a documentary about the Black Lives Matter movement while in the US.

The statement from Hashemi’s family said she was expected to make comment “in due course” and that she was planning to attend one of over two dozen events around the world that organizers had already planned for Friday to protest for her freedom.

“Just as America is aware of the harassment of the Black community by the police, America needs to start talking about the harassment of the Muslim community by the FBI,” read the statement.