US citizen formally charged with espionage in Russia

An American citizen held in Russian custody since Friday has been formally indicted on espionage charges, according to Russia's Interfax news agency.

Here's what we know

On Monday, Russia's FSB State Security agency revealed that it had arrested an American named Paul Whelan on Friday. Whelan, the FSB claimed, had been "caught spying" in Moscow. Whelan is a 48-year-old former Marine who lived in Michigan.

Russian authorities said that, if convicted, Whelan could face between 10 and 20 years in a Russian prison. Whelan's family has staunchly denied that he could be a spy. A man claiming to be Whelan's brother said that Whelan had been in Moscow for a friend's wedding.

On Wednesday, U.S. Ambassador to Russia Jon Huntsman met with Whelan. This was the first time he had been permitted to do so since Whelan had been detained on Friday.

For now, Whelan will be "quarantined" before being transferred to a general cell after Monday. A Russian lawyer named Vladimir Zherebenkov, who was appointed to represent Whelan, was quoted by Interfax as saying that Whelan would be held in Russian custody until at least Feb. 28.

What else?

Whelan's arrest came just two weeks after Russian national Maria Butina pled guilty to a conspiracy charge. Butina was arrested in July and charged with spying on U.S. citizens in Washington, D.C., at the behest of the Russian government. Butina had attended Republican political events under the guise of a pro-gun activist in order to gain access and influence in these circles.

Russia continues to deny that Butina was working as an agent on its behalf. Russian President Vladimir Putin has called these charges a "lie," and said, "I don't understand what they jailed her for. There are no grounds."

Whelan's arrest could be retaliation for Butina's imprisonment. There is no extradition treaty between the U.S. and Russia.