A lawyer for Nadia Savchenko, a Ukrainian air force officer who is on hunger strike in a Russian prison, says Russian authorities are investigating him for potential "extremist" language posted on his Twitter account.
Mark Feigin tweeted on April 1 that an investigator from Russia's Investigative Committee called him earlier in the day to inform him that the authorities were examining whether he violated Russian laws on extremism in connection with his Twitter activities.
There was no immediate confirmation from investigators that a probe is under way.
Feigin said authorities may try to remove him as Savchenko's attorney but vowed to "not back down" in his defense of the pilot.
Savchenko, 33, is charged with involvement in a mortar attack that killed two Russian journalists covering the conflict between government forces and Russian-backed separatists in eastern Ukraine.
She says she was kidnapped by separatists in June and illegally brought to Russia.
With reporting by TASS