A Moscow court has rejected an appeal by Wall Street Journal Reporter Evan Gershkovich and upheld an earlier ruling that he should remain in jail on espionage charges until late August.

“This was a procedural hearing, appealing the conditions of his continued detention,” explained U.S. Ambassador to Russia Lynne Tracy, “We were extremely disappointed by the denial of his appeal.”

Tracy says they will continue to fight for his release.

Tracy also urged Russian officials to release him along with other American citizens being detained, saying “such hostage diplomacy is unacceptable and we call on the Russian Federation to release him as well as (Canadian born) Paul Whelan, another U.S. citizen who has been wrongfully detained and we call for that release to occur immediately.”

The 31 year old U.S. citizen was arrested in late March while on a reporting trip.

Gershkovich’s arrest in the city of Yekaterinburg rattled journalists in Russia, where authorities have not detailed what, if any, evidence they have gathered to support the espionage charges.

Gershkovich and his employer have denied he spied in Russia.

He is being held at a Moscow prison, notorious for its harsh conditions.