American journalist Alsu Kurmasheva has been detained after visiting her family in the Russian city of Kazan and now faces charges, her colleagues say.
An editor for US-funded Radio Free Europe/Radio Liberty in Prague, she was temporarily detained on 2 June.
She was detained again on Wednesday and charged with failing to register as a foreign agent, which carries a jail term of up to five years.
Ms Kurmasheva is the second US journalist held in Russia this year.
Wall Street Journal Moscow correspondent Evan Gershkovich, 31, was arrested in March and charged with espionage. Earlier this month a court in Moscow rejected an appeal and ordered him to remain in detention.
His employer and the US government strongly deny the charges and say he is being held to be traded for Russian citizens in the custody of the US or its allies.
Alsu Kurmasheva, who holds both US and Russian citizenship, works for RFE/RL's Tatar-Bashkir service. Tatar and Bashkir are closely related languages spoken by indigenous peoples in two central Russian regions.
According to RFE/RL, Ms Kurmasheva, who lives in the Czech Republic, travelled to Kazan in late May for a family emergency. She was detained while waiting for her return flight and her Russian and American passports were confiscated.
Authorities charged her with failing to register as a foreign agent and with collecting information on behalf of foreign governments, according to Tatar Inform, a local state news site.
Dmitry Kolezev, a prominent Russian journalist, wrote that the law Ms Kurmasheva was charged under was written so broadly that collecting even basic information about military personnel, such as soldiers' names and unit numbers, could be prohibited. "They took another hostage," he added.
Ms Kurmasheva's work frequently focused on issues facing the ethnic minorities of central Russia.
Independent Russian media organisations and press freedom watchdogs say repressive laws are routinely used by Russian authorities to harass journalists and stile independent reporting.
A number of journalists and Kremlin critics have been labelled "foreign agents", including Nobel Peace Prize-winner Dmitry Muratov.
In September last year, Ivan Safronov, who worked for Kommersant and Vedomosti, was sentenced to 22 years in jail on treason charges.
In March, student Dmitry Ivanov was sentenced to eight and a half years in a prison colony for "distributing fake information" about the Russian army on the Telegram messaging app.
