A Moscow court has extended until January the detention of US reporter Evan Gershkovich, who was arrested in Russia earlier this year on spying charges.

The court said Mr Gershkovich's "period of detention" was extended by two more months until 30 January, 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.

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

Mr 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.

'Outrageous'

Both the Wall Street Journal and the US repeated their calls for Mr Gershkovich's immediate release after today'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".

A video released by the court showed Mr Gershkovich standing in a metal cage for defendants during today's hearing, wearing a checked shirt and dark hooded jacket.

The American, who previously worked for AFP, continued to report from Russia after the Kremlin launched its Ukraine offensive, despite many Western journalists leaving the country.

Russia claims it caught Mr Gershkovich "red-handed," but has not provided any public evidence of the allegations it has made against him.

He faces up to 20 years in prison if convicted.

US National Security Advisor Jake Sullivan said in July that Washington was engaged in diplomatic efforts to try to secure Mr Gershkovich's release through a possible prisoner exchange with Moscow.