A US citizen has been arrested in Russia accused of spying, it has been reported.

Vladimir Putin's feared FSB said the American had been detained on December 28, adding that a criminal case had been opened against him.

Paul Whelan was detained in Moscow by officers of the FSB, the country's domestic intelligence agency.

A statement read: "On October 28 members of the Federal security services of the Russian Federation arrested US citizen Paul Whelan in Moscow for carrying out espionage.

"The necessary investigations are ongoing."

Russia's relations with the US have soured since Moscow annexed the Crimean peninsula from Ukraine in 2014.

Since then the United States and other Western countries have imposed a wide-range of sanctions against Russian officials, companies and banks.

More to follow...