At least seven people were wounded by a man with a knife who went on a stabbing rampage in the northern Russian city of Surgut.
No one was killed in the attack in the central Siberian city, but four people were in serious condition, according to state-run Tass news agency, which cited a regional health official.
Islamic State says the man — shot dead by police — was a "soldier" of the extremist group. However, Russian authorities say psychiatric information on the assailant is being sought, suggesting they believe the claim by ISIS may be opportunistic.
A spokesman for Russia's Investigations Committee tells Reuters that it "is investigating attempted murder."
Russia's Interior Ministry said the assailant has been "tentatively identified" as a resident of the city in his 20s, but he has not been named. "The theory that the attack was an act of terrorism is not the main one," the ministry said.