Evan Gershkovich
© Evgenia Novozhenina/ReutersThe Wall Street Journal said the accusations against Evan Gershkovich's are 'demonstrably false'
A Russian court has extended the detention of Wall Street Journal (WSJ) reporter Evan Gershkovich by three months, ordering the 31-year-old American citizen to be held until August 30.

Gershkovich was arrested in March on espionage charges while on a reporting trip in Russia and formally detained in April. He, his employer and the US government have denied the charges.

Tuesday's pre-trial hearing was not announced in advance, and the entire case has been wrapped in secrecy.

Moscow has said the sensitivity of the espionage charges means the trial must be held in private and court documents are not being made public. Russian authorities have not detailed what - if any - evidence they have gathered to support the espionage charges.

Russia's state-owned TASS news agency said the session was closed because the reporter was accused of possession of "secret materials".

One Russian news agency, Interfax, quoted a court official as saying Gershkovich's parents were visiting Moscow and had been admitted to the court building but not into Tuesday's hearing.

The United States called for his immediate release after Russia's security service had sought to extend his detention.

"He shouldn't be detained at all. Journalism is not a crime. He needs to be released immediately," White House national security spokesman John Kirby told CNN.

"We're still going to work very, very hard to see if we can get him home with his family where he belongs."

'Deeply concerned'

US officials are still pressing for consular access to Gershkovich directly with the Russians, Kirby said.

"There is no grounds for denying consular access ... We really want to get that consular access going."

The US embassy in Moscow was quoted by WSJ as saying it was "deeply concerned by today's Russian court decision".

"The United States strongly objects to Russia's ongoing denial of consular access to Mr. Gershkovich. We reiterate that the claims against him are baseless and call for Mr. Gershkovich's immediate release," it said.

In a statement after Tuesday's hearing, the WSJ said, "While we expected there would be no change to Evan's wrongful detention, we are deeply disappointed. The accusations are demonstrably false, and we continue to demand his immediate release."

Gershkovich is the first US correspondent since the Cold War to be detained in Russia on spying charges. His arrest rattled journalists in the country and drew outrage in the West.

He is being held in Moscow's Lefortovo prison. US Embassy officials were allowed at least one prison visit to Gershkovich since his arrest in Yekaterinburg on March 29, but Russian authorities have denied permission for other visits.