In a dispute about wearing a mask to protect against the corona virus in Moscow, a man pulled a gun and shot at least two people.
Three other people were injured, said Mayor Sergei Sobyanin on Tuesday.
The alleged perpetrator was arrested;
the 45-year-old will be examined psychologically, it said.
Sobyanin spoke of a "tragedy".
The venue was one of the so-called multifunctional centers in the southeast of the Russian capital, where citizens can apply for and have their personal documents processed.
The suspect is said to have refused to put on mouth and nose protection despite being asked by the staff.
Then he pulled the pistol and shot.
The Interior Ministry said there was also a ten-year-old girl among the injured.
Sobyanin said the doctors were doing everything they could to treat the injured.
The head of the largest city in Europe expressed his condolences to the families of those killed.
In Russia there had recently been several incidents, including protests by opponents of hygiene regulations in the corona pandemic.
In November of last year a person who refused to wear a mask stabbed a bus traveler in St. Petersburg after he had pointed out the obligation to wear mouth and nose protection.