Wall Street Journal reporter Evan Gershkovich lost his appeal against the extension of pre-trial detention in Moscow on Thursday on spying charges, which he denies.

Gershkovich's detention, at the notorious Lefortovo prison in Moscow, was extended last month to August 30. He faces up to 20 years in jail on espionage charges, which he and his employer vehemently contest.

Gershkovich was in court for the decision, in a glass cage, wearing a dark t-shirt and jeans.

The US ambassador to Russia, Lynne Tracy, was also at the hearing at Moscow City Court, as were his parents, Ella Milman and Mikhail Gershkovich.

Russia's main security service, the FSB, has claimed that Gershkovich, a correspondent based in Moscow, had been trying to obtain state secrets.

His arrest in March was the first detention of an American reporter in Russia on allegations of spying since the Cold War, rattling White House officials and further straining ties between Moscow and Washington.

The US State Department has officially designated Gershkovich as wrongfully detained in Russia. US President Joe Biden has also been blunt about Gershkovich's arrest, urging Russia to "let him go."