Moscow, Russia - A Moscow court on Tuesday said it had extended until January the detention of Wall Street Journal reporter Evan Gershkovich, who was arrested in Russia in March on spying charges.

The court said Gershkovich's "period of detention" was extended by two more months until January 30, in what the Wall Street Journal, his employer, called a "brazen and outrageous attack on a free press."

The 32-year-old correspondent, the Wall Street Journal and the US government have all rejected the spying allegations.

The hearing was held behind closed doors, and no press were allowed inside.

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The US Embassy in Moscow said its officials were able to attend the hearing.

AFP saw a handful of reporters waiting outside the courtroom.

The latest extension of Gershkovich's detention was almost certain, as Moscow rarely releases people imprisoned while awaiting trial on serious charges.

Gershkovich was arrested during a reporting trip at the end of March in the Urals city of Yekaterinburg, becoming the first Western reporter to be jailed on spying charges in Russia since the Soviet era.

He has been held at Moscow's notorious Lefortovo prison and faces 20 years behind bars if convicted.

Both the Wall Street Journal and the US repeated their calls for Gershkovich's immediate release after Tuesday's hearing.

"The accusations against him are categorically false and his continued imprisonment is a brazen and outrageous attack on a free press, which is critical for a free society," the Wall Street Journal said in a statement.

The US Embassy in Moscow said it was "deeply concerned by the court's decision... We reiterate our call for his immediate release."