Horrific new details of how a nanny beheaded a four-year-old girl and paraded through the streets of Moscow with her severed head have been revealed.

The woman, dressed in a burka, threatened to blow herself up as she walked near Oktyabrskoye Pole metro station holding up the little girl's head.

Investigators claim she murdered the girl, who is believed to have learning difficulties, after starting a fire at the child's family home in a block of flats.

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A burka-clad babysitter has been arrested in Moscow after she walked through the streets carrying the severed head of a four-year-old girl

The nanny, Gyulchehra Bobokulova, 38, from Uzbekistan, has been arrested.

It is now known that the beheaded remains of the girl, identified as Anastasia (Nastya) Meshcheryakova, were discovered inside her cot. Her body had been dressed in her night clothes, consisting of a T-shirt and shorts.

According to local media, Bobokulova shouted in the street: 'I hate democracy. I am a terrorist. I want you dead.

'You have become so hardened, you have eliminated so many of us. Look I am a suicide bomber, I will die, doomsday will come in a second.'

She pulled the severed head out of a bag and walked near the metro station entrance in north-west Moscow.

Video of the dead girl's mother, Ekaterina Meshcheryakova, collapsing in the street upon hearing the horrific news has emerged. She was taken to hospital in an unconscious condition.

Anastasia also had a father, Vladimir Meshcheryakov, who is a technician at a mobile phone company, and a brother Konstantin, 15.

The main entrance to the block of flats is being guarded by armed police.

Eyewitness Alexandra Shuvalova, a student from the capital, said: 'When I got close to the metro, I saw a woman running along the street.

Eyewitnesses say the woman shouted 'Allahu Akbar' as she appeared near Oktyabrskoye Pole metro station in the northwest of the Russian capital and threatened to blow herself up

Sources say the babysitter told interrogators she did not want to hide from police, and aimed to draw maximum attention to what she has done

The woman was seen pulling the severed head out of a bag and walking around near the entrance to the metro station as police moved in

'I could see that she had hair in her hands or something like that.

'She was waving this thing and screaming something and drawing some shapes in the air.

'This woman either had a birthmark or a wart on her right cheek. It was a distinctive feature because she was dressed in entirely in black.

'I realised it wasn't a wig as I thought initially, but a head - that's why blood was dripping on her shoes and skirt.

'I stopped, had a cigarette, tried to get my breath back to normal because I was so shocked.'

She claimed a security guard and two policeman missed the chance to detain her.

Alexandra added: 'People ran away from her. I saw five people fleeing. And no one tried to stop her - not security guards at a cafe, nor at a shop.

'One of the guards who saw her, ran to the building to tell someone about her. He didn't try to do anything on his own.'

The child, who has been identified as Anastasia (Nastya) Meshcheryakova, whose nanny Gyulchehra Bobokulova is thought to have killed her

The victim was a girl identified as Anastasia (Nastya) Meshcheryakova - and the child's 38-year-old nanny Gyulchehra Bobokulova (left), from Uzbekistan, has been arrested. The girl's mother Ekaterina is pictured right

'I heard her yelling 'Allah Akbar' at least three times. And hitting herself on her chest.

'She was yelling something in her language. She ran to a cafe and started shouting: 'It's all you! All you!'

According to local reports, she later told police she killed the girl because of her own husband's infidelity. Investigators immediately ordered a psychiatric test of the woman in a bid to understand her motives.

One eyewitness at the underground station told MK how the woman screamed: 'My child was killed…I will blow up everyone.' She also shouted: 'I hate democracy'.

A journalist working for RBC daily, said she had heard the woman screaming 'Allahu Akbar' (God is Great).

'I was on my way to the metro station from home,' Polina Nikolskaya said.

Another witness said the woman shouted that she would 'kill everyone, blow up everyone'.

'She was standing near the metro entrance and caught my attention because she was screaming Allahu Akbar,' she said.

Mother Ekaterina and father Vladimir Meshcheryakov of four-year-old Anastasia

The suspect shouted that she had killed the child and was seen praying shortly before officers swooped at Oktyabrskoe Pole

One eyewitness at the underground station told MK how the woman (pictured left and right holding the severed head) screamed: 'I will blow up everyone'

'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.'

Some said the woman had paced up and down for some 20 minutes before she was detained near the station.

In further footage from the scene, the woman can be heard shouting about the end of the world while proclaiming herself a terrorist.

The station was closed to passengers for some time, but no explosives were found on her.

Another eyewitness said: 'She came to the entrance of the metro station Oktyabrskoye Pole with a red bag, from which she pulled out the child's head.

I could see that she had hair in her hands or something like that. 'She was waving this thing and screaming something and drawing some shapes in the air...I realised it wasn't a wig as I thought initially, but a head - that's why blood was dripping on her shoes and skirt Eyewitness Alexandra Shuvalova

'She walked down the street for a long time and was shouting something. But no one challenged her. Everyone was afraid.'

Dramatic footage shows the moment police sprinted in towards the woman and tackled her to the ground.

Emergency services had earlier been called to an apartment nearby amid reports of black smoke billowing out of windows.

Firefighters rescued four people and put out the blaze - but then found the child's beheaded body

Witness Alyona Kuratova told independent Dozhd TV that the woman was holding the head by its hair.

Kuratova described scenes of chaos, with police cars and ambulances arriving at the scene and some people yelling: 'terror attack, terror attack.'

She said she could not make out what the woman shouted but some media reported that she yelled 'Allah Akbar''- Arabic for 'God is greatest' - and threatened to blow herself up.

Investigators claim that the babysitter waited until she was alone with the child in the apartment before carrying out the murder and starting a fire.

Dramatic footage shows the moment police sprinted in towards the woman and tackled her to the ground

The woman was surrounded by police officers and bundled to the ground during the dramatic arrest in Moscow

Emergency services had earlier been called to an apartment nearby amid reports of black smoke billowing out windows

Firefighters rescued four people and put out the blaze - but then found the child's beheaded body

A source in the Investigative committee told TASS: 'She waited until the parents with the elder child left the flat, then for unknown reason she killed the child, set fire to the apartment and left the scene.

'She was detained at the metro station Oktyabrskoe Pole.'

The dead girl, who is said to have had learning difficulties and could not walk. Her family, from the Oryol region, was renting the apartment.

She suffered damage because of birth problems in August 2011.

The family took her for treatment to China - and were saving money to travel for subsequent care in Germany.

The parents told police the nanny had been working for them for 18 months.

Sources say the babysitter told interrogators she did not want to hide from police, and aimed to draw maximum attention to what she has done.

She had not intended to ignite the flat deliberately and destroy evidence, she said, according to the source, and wanted the parents to know who had killed their daughter.

The woman had a valid residency permit for Russia but was working illegally. She had no work permit, said officials.

The nanny faces up to 20 years in jail if she is deemed psychologically fit to stand trial.

This afternoon, the investigation was taken over by the FSB, Russia's powerful domestic secret service, once headed by Vladimir Putin. Police are not currently treating the incident as terrorism.

Police descended on the scene as an investigation got underway at the metro station in the wake of the arrest

Detectives cordoned off the station to investigate. The nanny faces up to 20 years in jail if she is deemed psychologically fit to stand trial.

A Russian police officer stands at the site where a woman suspected of murdering a young child was detained

Employees of the Russian Investigative Committee near an entrance to Oktyabrskoye Station

LifeNews claimed: 'Investigators suspect that Gulchekhra had manic psychosis developing for a period of time.'

A law enforcement source said the woman was suspected of handling 'explosive elements' at the flat which was engulfed in flames.

But 'it might be an inflammable liquid that she used to set the apartment on fire where she killed four-year-old Nastya M.'

The security services are hunting for the woman's husband. A source said she may have been on 'light drugs'.