Paul Whelan, a 48-year-old American, has been formally charged with espionage in Russia.
He was arrested last week after being accused of being on a "spy mission."
"The investigation department of the Federal Security Service of Russia initiated a criminal case against a U.S. citizen under article 276 of the Criminal Code of the Russian Federation," Russian state media agency Interfax said in a statement Thursday.
"The investigation is underway."
Whelan _ who denies the accusations _ will remain in custody until Feb. 28 in Moscow, according to Vladimir Zherebenkov, the Russian lawyer representing Whelan.
"Today I sent by mail an appeal complaint in which I ask the Moscow City Court to cancel the decision on the arrest of Whelan and to elect another preventive measure in the form of bail," Zherebenkov told Interfax.
Whelan's family took to Twitter to express their concern for his "safety and well-being."
His "innocence is undoubted and we trust that his rights will be respected," the family said.
If convicted, Whelan faces 20 years in prison.
