Police in Moscow have arrested a woman after she was seen walking near a metro station with a child's severed head in her hands.
CCTV shows the woman, who was dressed in a hijab, being wrestled to the ground by a police office. She has since been arrested on suspicion of murder.
It is believed the woman, believed to be the victim's nanny, is believed to have killed the child before setting fire to its parent's apartment.
The woman, the BBC reports, has been placed in psychiatric care to determine whether she is capable of understanding her actions, the Moscow Investigative Committee said in a statement.
Police launched an investigation after the charred remains of a child aged three to four, whose body bore traces of a violent death, was discovered in an apartment in north-western Moscow.
"According to preliminary information, the child's nanny, a citizen of one of the Central Asian states born in 1977, waited for the parents and elder child to leave the flat and then, for reasons not established, murdered the infant, set fire to the flat and left the scene," the police statement added.
Police sources told Russian news agencies that the victim had been decapitated and the head removed from the scene by the nanny.
The suspect was named by Russian media as Gyulchekhra Bobokulova, from the former Soviet republic of Uzbekistan.
Russia's tabloid news website Life News reported that the victim was a girl.
According to Life News, a policeman asked to see the woman's identity documents outside Oktyabrskoye Polye metro station, when she removed the child's head from her bag and threatened to blow herself up. No explosives were found on the woman, the website said.
Amateur video posted online shows a black-clad woman outside a metro station shouting the Islamic phrase "Allahu Akbar" (God is Great).
"I am a terrorist," she cries. "I am your death."
Russian journalist Polina Nikolskaya witnessed the incident and told Reuters: "I was on my way to the metro station from home. She was standing near the metro entrance and caught my attention because she was screaming Allahu Akbar.
"I saw that she had a bloodied head in her arms but I thought it was not real. People in the crowd said it was real."
Other witnesses, the BBC reported, claimed the woman walked up and down outside the metro station for some 20 minutes, shouting and brandishing the head.
The phrase "Allahu Akbar" has been trending on Russian social media, in a country with a recent history of violent Islamist militancy.