WASHINGTON (AFP) - A man who said he is the brother of an American arrested in Moscow on espionage charges posted on Tuesday (Jan 1) a statement from the family protesting his innocence.

"We have read reports of the arrest in Moscow of Paul Whelan, our son and brother," said the statement posted on Twitter by Mr David Whelan, who said he is the brother of Paul.

"Paul is a retired Marine and was visiting Moscow to attend a wedding," it continued, adding that he stopped being in communication with his family on Dec 28, "which was very much out of character for him even when he was travelling."

They added that they had learned of the arrest through the media on Monday morning and had been in touch with US lawmakers, as well as the State Department.

"We are deeply concerned for his safety and well-being. His innocence is undoubted and we trust that his rights will be respected," the statement said.

SPY SCANDALS

The arrest marked the latest in a series of espionage cases between Russia and the West.

The FSB domestic security service said the American was arrested on Friday "while carrying out an act of espionage".

A criminal case had been opened, the FSB said in a statement, under Article 276 of the Russian Criminal Code, which allows for prison sentences of up to 20 years.

In Washington, the State Department said it had been formally notified by Russia's Foreign Ministry and was seeking access to the detained American.

The arrest came with Moscow embroiled in a number of spy scandals with the West and after President Vladimir Putin accused Western nations of using espionage cases to try to undermine an increasingly powerful Russia.

US intelligence services have accused Moscow of interfering in the 2016 presidential election, and in December a young Russian, Maria Butina, pleaded guilty in a federal court in Washington to acting as an illegal foreign agent.

Butina faces up to six months in prison, followed by likely deportation.

Russian military intelligence agents were also accused in the poisoning last year of former double agent Sergei Skripal and his daughter in Salisbury, England.

The Skripals survived, but a local woman died after picking up a discarded perfume bottle that police think was used to carry out the attack.