BERLIN — The killing of a former Chechen separatist commander in central Berlin has raised concerns that Russia may have deployed an agent to a European nation to target a Kremlin opponent, a tactic it has been accused of using many times in the past.

The victim, Zelimkhan Khangoshvili, who fought against Russian troops in the second Chechen war 20 years ago, was on his way to Friday prayers last week when he was shot in the head twice by a bicycle-riding man using a handgun with a silencer, according to witness accounts cited in the German news media.

The Russian government in 2006 legalized the killings abroad of people who were judged to pose terrorist threats, resuming a Soviet-era practice.

The Kremlin has never acknowledged using the authority granted under the law and has denied specific accusations, including that it tried to kill a former double agent, Sergei V. Skripal, with a nerve agent in Britain last year. In Ukraine, the authorities have reported a number of killings and attempted killings that they attribute to Moscow.