An American citizen is being wrongfully detained in junta-ruled Myanmar, a US embassy spokesperson told AFP on Friday.
"We are aware of the wrongful detention of a US citizen in Burma," the spokesperson told AFP, using the country's former name.
Several foreigners have since been arrested in the junta's crackdown on dissent.
The spokesperson did not give details on how long the US citizen had been detained or whether they had been charged by junta authorities.
Staff were "providing all appropriate consular assistance", they said.
On Tuesday, President Joe Biden opened the way for sanctions against governments that unjustly imprison Americans and ordered more detailed travel warnings after a series of high-profile detentions.
The move came after wide media coverage of the detention in Russia on drug charges of basketball star Brittney Griner, whose wife initially said Biden was not doing enough.
Myanmar has been included in the initial group of nations that will bear a "D" mark for detention risk, along with China, Iran, North Korea, Russia and Venezuela.
In an updated travel advisory, the State Department said it had determined that "at least one US national" was wrongfully detained in Myanmar.
Polish photojournalist Robert Bociaga and Japanese journalist Yuki Kitazumi were both detained during the early protests against the coup.
US citizen Nathan Maung was arrested in March last year during a police raid on the local media outlet he ran and charged with encouraging dissent against the military.
He was released months later.
Fellow journalist and US citizen Danny Fenster was detained in May 2021 and in November was handed an 11-year sentence for unlawful association, incitement against the military and breaching visa rules.
Days later he was pardoned and deported from Myanmar.
