A Moscow court on Thursday ordered US journalist Evan Gershkovich be detained for two months on suspicion of spying, pending a possible trial.

Gershkovich, a reporter for the Wall Street Journal, has been placed in detention "for a period of one month 29 days, that is until May 29, 2023," the Moscow Lefortovsky district court said in a statement.

His detention may be extended at the end of this period.

The state-run TASS news agency cited a law enforcement source as saying Gershkovich's case has been classified "top secret" and that the US journalist said he was not guilty of the allegations.

Russia's FSB security service announced Gershkovich's arrest on Thursday, saying he was "suspected of spying in the interests of the American government".

The Wall Street Journal said it was deeply concerned for his safety and media watchdog Reporters Without Borders said it was "alarmed by what looks like retaliation".

Gershkovich worked for AFP in Moscow before joining The Wall Street Journal early last year.

A fluent Russian speaker, he was previously a reporter based in the Russian capital for The Moscow Times, an English-language news website.