Police in the Russian capital Moscow have arrested a woman on suspicion of murdering a child after she was found apparently carrying a severed head.
The woman, believed to be the victim's nanny, is suspected of killing the child before setting fire to its parents' apartment.
CCTV appears to show the woman, dressed in a hijab, walking near a metro station with a head in her hands.
A police officer then intercepts her and wrestles her to the ground.
The suspect has been placed in psychiatric care to determine whether she is capable of understanding her actions, the Moscow Investigative Committee said in a statement (in Russian).
A criminal investigation was launched after the discovery of the remains of a child aged three to four, whose body bore traces of a violent death, in a charred flat on Narodnoye Opolcheniye Street in north-western Moscow, it added.
"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," it added in the statement.
Police sources told Russian news agencies that the victim had been decapitated and the head removed from the scene by the nanny.
'I am your death'
The suspect has been named by Russian media as Gyulchekhra Bobokulova, from the former Soviet republic of Uzbekistan.
Russia's tabloid news website Life News, which specialises in crime coverage, reports that the victim was a little girl.
According to Life News, a policeman asked to see her identity documents outside Oktyabrskoye Polye metro station, at which point she pulled the head of the child out of a bag and began screaming that she would blow herself up.
No traces of explosives were found on the suspect after her arrest, the site adds.
Amateur video posted online shows a black-clad woman, apparently the suspect, 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. She 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 says 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.
In 2010, a twin bombing by women suicide attackers on the Moscow metro killed at least 38 people while in 2011, a bomb at Domodedovo airport killed 37 people.
Islamist groups from restive parts of Russia's North Caucasus region such as Dagestan and Chechnya have been behind most of the attacks.
Uzbekistan, which like other Central Asian states has a Muslim majority, has long supplied migrant labour for the Russian capital.