BANGKOK (AP) — The U.S. State Department said Friday it is deeply concerned about the detention of two American citizens who have been working as journalists in Myanmar, and is pressing that country’s military government for their immediate release.

It said in a statement that it will keep seeking the release of Daniel Fenster and Nathan Maung “until they are allowed to return home safely to their families.”

Human rights organizations and groups promoting freedom of expression have been calling for the release of both men, as well as all other journalists being held by Myanmar’s military government.

Fenster, 37, was detained at Yangon International Airport on Monday as he was preparing to board a flight to Kuala Lumpur, Malaysia, en route to the Detroit area to see his family. He is the managing editor of Frontier Myanmar, a news and business magazine that is published in both English and Burmese and also online.

“We are obviously very concerned about Danny and want to know why he has been detained,” the magazine’s editor-in-chief, Thomas Kean, said Friday. “So far we have not been able to get any information from the authorities and we still haven’t had the chance to meet him.”

Frontier Myanmar said on the day Fenster was detained that it understood he was taken to Insein Prison in Yangon, which over decades has housed thousands of political prisoners, including many from the current movement that is actively protesting military rule.

Maung and Myanmar national Hanthar Nyein, co-founders of the local Myanmar news website Kamayut Media, were arrested on March 9, according to the New York-based Committee to Protect Journalists, citing accounts in Myanmar media. The group said it had reports that Maung, the website's editor-in-chief, and Hanthar, a news producer, had been physically mistreated by guards in their first few weeks at Insein Prison.

The State Department statement said consular officers from the U.S. Embassy in Yangon had paid a virtual visit to Maung this past Monday but so far have not been granted access to Fenster. It said it urged the authorities “to grant consular access, as required by the Vienna Convention on Consular Relations, without delay, and to ensure proper treatment of both Nathan and Daniel while they remain detained.”

It said "Free and independent media is indispensable to building prosperous, resilient, and free societies,” and that the arrests and use of violence against journalists in Myanmar “constitutes an unacceptable attack on freedom of expression.”

Two other foreign journalists have also been arrested by the military junta that took power in February after ousting the elected government of Aung San Suu Kyi. Freelancers Robert Bociaga of Poland and Yuki Kitazumi of Japan have since been deported from the country.

“The ongoing persecution, intimidation, harassment and violence faced by journalists in Myanmar constitutes a clear attempt by the military authorities to suppress peaceful dissent and obscure violations committed by security forces in the wake of the 1 February coup,” the human rights group Amnesty International said in a statement this week. “The nationwide crackdown has resulted in widespread denial of the rights to freedom of expression and access to information.”

It said that according to Myanmar’s Assistance Association for Political Prisoners, 88 journalists have been arrested since the army’s takeover, with more than half still in detention, and 33 in hiding.

According to the Assistance Association, which has kept a detailed tally of arrests and deaths since the military takeover, more than 4,300 people are in detention, including 104 who have already been sentenced.

Reporter Without Borders and PEN International are among other groups calling for the release of the journalists.

Grant Peck, The Associated Press