Russian news agencies are reporting that police have arrested a woman who was waving the severed head of a small child outside a Moscow subway station.

The reports cite law enforcement sources and eyewitnesses. Videos posted on Russian news websites show the woman dressed all in black and shouting "I am a terrorist," although most of what she says is incomprehensible.

The Investigative Committee released a statement saying a woman was arrested Monday on suspicion of killing a child aged 3 or 4 in an apartment near the metro station in northwestern Moscow and then setting the apartment on fire. The statement said the woman was believed to be the nanny.

The official report did not link the two incidents.

The investigators said the woman appeared to be mentally unstable.