Moscow has angrily told the US embassy to "mind your own business" after Washington's diplomatic mission raised concern about curbs on media freedom in Russia.
Rebecca Ross, the spokeswoman for the US embassy, on Tuesday expressed concern about a clampdown on journalists in Russia.
"Watching arrest after arrest of Russian journalists – it's starting to look like a concerted campaign against #MediaFreedom," she tweeted.
"Mind your own business," the Russian foreign ministry tweeted late Tuesday.
Earlier that day the FSB security agency, the successor to the Soviet-era KGB, arrested a respected former journalist, Ivan Safronov, 30, on suspicion of state treason.
His detention sparked an uproar among supporters and journalists who say his arrest is punishment for his coverage of Russia's defence sector.
A member of Safronov's defence team, Yevgeny Smirnov, has said the former journalist, who used to work for Kommersant and Vedomosti newspapers, is suspected of cooperating with Czech intelligence since 2012.
The FSB investigators believe that the Czech intelligence acts under the guidance of the United States, Smirnov told AFP.
The FSB says that Safronov has collected confidential data about the Russian military, defence, and security and handed it over to the intelligence of a Nato member country.
On Monday, a reporter from the northwestern city of Pskov was fined nearly $7,000 for "justifying terrorism", in a case that sparked an outcry.
Prosecutors had requested that Svetlana Prokopyeva be sentenced to six years in prison for a commentary about a bomb attack.
All major TV stations are under state control in Russia.
Journalists working for print and online outlets have recently complained about increasing curbs on press freedoms and pressure from the Kremlin.