MOSCOW -- Jailed Russian opposition politician Vladimir Kara-Murza reportedly has been charged with high treason.
Russian media quoted unnamed law enforcement officials and sources as saying that the high-treason charge against Kara-Murza stems from his alleged cooperation with organizations in a NATO member for many years.
If convicted, the staunch Kremlin opponent faces up to 20 years in prison.
The 41-year-old politician was detained in April and sentenced to 15 days in jail on a charge of disobeying a police order. He was later charged with spreading false information about the Russian military while speaking to lawmakers in the U.S. state of Arizona.
Kara-Murza has rejected the charge, calling it politically motivated.
His lawyer, Vadim Prokhorov, told TASS on October 6 that the treason charge against Kara-Murza stems from speeches he gave at events in Lisbon, Helsinki, and Washington that criticized the Kremlin's rule.
“These speeches did not carry any threat to the country; it was public, open criticism,” Prokhorov said, according to TASS.
His arrest comes amid a mounting crackdown on Russian opposition figures and any dissent to the ongoing war in Ukraine that Moscow launched against its neighbor on February 24.
In August, Kara-Murza was additionally charged with carrying out activities of an undesirable organization for taking part in organizing a conference in Moscow last year to support political prisoners in Russia that was sponsored by the foreign-based Free Russia Foundation. That group has been declared "undesirable" in Russia.
The "undesirable organization" law, adopted in 2015, was part of a series of regulations pushed by the Kremlin that squeezed many nonprofit and nongovernmental organizations that received funding from foreign sources -- mainly from Europe and the United States.
Russian lawmakers have since dramatically widened the scope of the law, including to bar Russian nationals and organizations anywhere in the world from taking part in the activities of such "undesirable" groups.
In early March, President Vladimir Putin signed a law that calls for lengthy prison terms for distributing "deliberately false information" about Russian military operations.
The law envisages sentences of up to 10 years in prison for individuals convicted of an offense, while the penalty for the distribution of "deliberately false information" about the Russian military that leads to "serious consequences" is 15 years in prison.
A close associate of slain opposition leader Boris Nemtsov, Kara-Murza is best known for falling deathly ill on two separate occasions in Moscow -- in 2015 and 2017-- with symptoms consistent with poisoning.
Tissue samples smuggled out of Russia by his relatives were turned over to the FBI, which investigated his case as one of "intentional poisoning."
U.S. government laboratories also conducted extensive tests on the samples, but documents released by the Justice Department suggest they were unable to reach a conclusive finding.