PRAGUE -- The U.S. ambassador to Russia has urged Moscow to either produce evidence in the case of jailed U.S. citizen Paul Whelan or release him.

"If there's a case, I think the evidence would have been brought forward by now," Ambassador Jon Huntsman told RFE/RL's Russian Service in an exclusive interview in Prague on April 12. "So, for me, as the senior American official in Russia, I hope that he is released as quickly as possible."

"If there is no evidence, and the Russians have not shown that there is any evidence so far, then let's move on," Huntsman added. "Let's move on and quit playing these games."

The comments come at a time of high tension between Moscow and Washington over, among other things, Russia's 2014 annexation of Ukraine's Crimean Peninsula and its military involvement in the conflict in eastern Ukraine that has left more than 10,300 people dead.

Whelan, a former U.S. Marine who holds U.S., Irish, Canadian, and British citizenship, was arrested in Moscow on December 2018 and has been charged with spying. He is currently being held in pretrial detention.

Whelan's family says that he was in Moscow to attend a wedding, and they deny the Russian allegations. If convicted, he could face up to 20 years in prison.

Whelan's detention came weeks after a Russian woman, Maria Butina, pleaded guilty in a U.S. court to acting as an agent for the Kremlin.

The Kremlin has denied that Butina is a Russian agent and has organized a social-media campaign to secure her release.

In the past, Russia has arrested foreigners with the aim of trading prisoners with other countries.

Huntsman also said the April 11 decision by a Moscow court to release another American, investment banker Michael Calvey, to house arrest pending his trial on embezzlement charges was "a step in the right direction."

"We hope, as I know his family does, that this is resolved as quickly as possible," Huntsman said.

The full interview with Huntsman will be published on April 13.