U.S. journalist Evan Gershkovich on Thursday lost a new appeal in a Moscow court against his pre-trial detention on espionage charges. 

The Wall Street Journal reporter was arrested by Russia’s FSB security service late March. His defense appealed for Gershkovich to be released from Moscow's Lefortovo prison while awaiting trial on charges that could have him sentenced to up to 20 years in prison. 

"The court considered the complaint brought by Gershkovich's defense against the decision to extend his ... detention, and ruled that the initial decision should be left unchanged and the complaint of the defendant's defense should not be satisfied," the judge said as quoted by AFP. 

Gershkovich, 31, is the first foreign journalist arrested in Russia on spying charges since the collapse of the Soviet Union. His arrest sparked international outcry with Washington stating he was wrongfully detained. 

"We were extremely disappointed by the denial of his appeal," U.S. ambassador to Russia Lynne Tracy told journalists outside Moscow City Court.

"Despite Russian officials' public assertions about Evan's activities, let me reiterate the U.S. government's firm position: the charges against him are baseless," she added. "He's an innocent journalist, who was carrying out journalistic activities and has been wrongfully detained".

The ambassador added that Russian authorities had denied three consular visits to Gershkovich, partly as the result of a visa disagreement with the United States involving Russian journalists. Gershkovich's parents, who left the Soviet Union and emigrated to the United States in 1979, were both present in the courtroom to support their son.