On 31 December, the Russian Federal Security Service (FSB) detained Paul Whelan, accusing him of espionage and launching a criminal case against him.

US State Secretary Mike Pompeo said the US demands the immediate return of the detained Paul Whelan and seeks an explanation of why he was arrested. READ MORE: US Man Accused of Espionage in Russia Was Dismissed by Marines for Theft — Media

Exhibition performance of border guards in Crimea ©
Sputnik / Maks Vetrov FSB Border Service Detains Up to 3,000 Trespassers Annually
He added that Washington hopes to gain consular access to the detained US citizen over the next few hours.
Reporting about the Whelan's arrest, the Russian Security Service (FSB) announced that a criminal case under the article "espionage" had been initiated against him.
The article, according to which the criminal case was initiated, allows for punishment in the form of imprisonment for a term of 10 to 20 years.
Commenting on the issue, the Russian Foreign Ministry stated that the US Embassy had been notified of the detention of its citizen in accordance with consular convention. This was also confirmed by a representative of the US State Department, who said that the Russian Foreign Ministry has officially notified the US of the detention of an American citizen in Moscow.
Paul's twin brother David Whelan claimed that he was not guilty and said he travelled to Moscow to attend a wedding ceremony, CNN reported earlier.
According to David, Paul was a retired marine who served several tours in Iraq.
However, Washington Post reported that in 2008 Paul Whelan was dismissed from the US Marine Corps for misbehaviour, after being convicted of several counts of larceny.Source: sputniknews.com