The Russian journalist Tatyana Feldenhauer has been seriously injured after an unidentified attacker stabbed her in the throat.
The incident took place in the editorial offices of the Echo of Moscow radio station after 12 noon local time. Ms Felderhauer is deputy editor in chief of the leading liberal media outlet.
The man, who had broken into the editorial office, was held by colleagues and later arrested.
Ms Feldenhauer is in hospital and receiving treatment, which includes a catheter to bypass the neck wound. According to the editor in chief, Alexei Venediktov, the injuries are not life-threatening.
The Ria Novosti state news agency has reported a source claiming that the assailant may have been motivated by an undisclosed “personal conflict”. A spokesman for the Russian Prosecutor-General's office, Alexander Kurennoi, said on Facebook the attack was an outrageous act.
Fellow Echo of Moscow journalist Vitaly Ruvinsky posted a picture on Twitter showing a man accused of being the attacker.
Other images shared on social media showed blood splashed across the floor of the editorial offices, a large knife and Russian police officers with a suspect in handcuffs.
Echo of Moscow is owned by the state-run gas giant Gazprom, but it does give air time to journalists and commentators who are fiercely critical of the Kremlin and has been described in the past as "Russia's last independent radio station".
One of the station's regular broadcasters, Yulia Latynina, said earlier this year she had been forced to flee Russia after a series of attacks, including the torching of her car.