Moscow, Russia - Lawyers representing Wall Street Journal reporter Evan Gershkovich, detained in Russia on spying charges, have appealed the latest extension of his arrest, Russian news agencies reported Friday.

Gershkovich, who continued reporting from Russia after the Kremlin launched its large-scale offensive in Ukraine, became the first Western journalist to be arrested and accused of spying since the Soviet era.

He was arrested on March 29 during a reporting trip in the Urals and has since been held behind bars.

According to the website of Moscow's Lefortovo Court, where Gershkovich has appeared before judicial officials, his defense team have appealed a recent decision to keep him in detention until August 30.

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Earlier this week the same court extended his arrest by three months in a hearing behind closed doors.

The United States has called for his "immediate release" and his case has been seen as a serious breach of media freedoms.

Gershkovich is held in Moscow's notorious Lefortovo Prison, which is known for keeping detainees in near-total solitude.

US Ambassador Lynne Tracy visited Gershkovich mid-April and said the reporter was "in good health." His only public appearance so far was during a court hearing on April 18, when his appeal against pre-trial detention was shot down.

Russian authorities have since denied two consular visits to Gershkovich as part of a visa disagreement with the US involving Russian journalists.