United States citizen and managing editor of Frontier Myanmar Danny Fenster "was detained at Yangon International Airport this morning," his employers said in a statement on their verified Twitter account.

"We do not know why Danny was detained and have not been able to contact him since this morning. We are concerned for his wellbeing and call for his immediate release," it added.

Myanmar has been in uproar since the February 1 coup, with near-daily protests and a nationwide civil disobedience movement.

More than 800 people have been killed by the military, according to a local monitoring group.

The press has been caught in the junta's crackdown as the military attempts to tighten control over the flow of information, throttling internet access and revoking the licenses of five local media outlets.

At least 34 journalists and photographers remain in custody across Myanmar, according to monitoring group Reporting ASEAN.

Frontier said it understood Fenster had been transferred to Yangon's notorious Insein Prison.

Japanese reporter Yuki Kitazumi was detained by authorities in Myanmar last month and was held in the same prison until being freed last week.

In March a BBC journalist was briefly detained after being seized by plainclothes officers while reporting outside a court in the capital Naypyidaw.