An Uzbek babysitter who confessed to the crime of decapitating a four-year-old girl under her care allegedly because she was "ordered'' by Allah to carry out the grisly killing has been formally charged with murder in the case, according to reports.

Vladimir Markin, a spokesman for Russia's Investigative Committee, confirmed on Friday that the charges have been filed against 38-year old Gyulchekhra Bobokulova, an Uzbek citizen and a mother of three.

Bobokulova told reporters on Wednesday that ''Allah ordered'' her to cut off the head of the girl named Nastya Meshcheryakova, who suffered from epilepsy.

Witnesses saide the Uzbek nanny was dressed in black and shouted "Allahu Akbar!" as she stood outside of the Oktyabrskoye Polye metro station Monday morning, waving the girl's severed head in the air.

She threatened to blow herself up when asked by police to provide proof of her identity. Video footage also shows the woman proclaiming, "I am a terrorist. I am your death."

In the video during an apparent police interrogation, Bobokulova said she did the brutal act to avenge the killing of Syrian Muslims by Russia through its airstrikes.

In addition to killing the girl, Bobokulova was also accused of setting the family's apartment on fire before running off with the child's head. Firefighters found the headless body of the little girl in responding to the blaze.

Prosecutors told the Presnensky District Court that they think individuals who are still at large "incited'' Bobokulova to kill the child.

Authorities said the woman suffers from mental health problems and is undergoing psychiatric evaluation. She was said to be under the influence of psychotropic drugs at the time of the crime.

Bobokulova, who has three sons, had kept her mental illness a secret. She had been divorced, and was in a relationship with another man, who soon went back to his wife, the Daily Mail reported.

In a related development, Bobokulova's eldest son Rakhmatillo Ashurov, 19, was reportedly arrested by authorities over his "connections'' with the extremist group Islamic State (ISIS).

He is currently held in detention in his native Uzbekistan on a 15-day "administrative punishment'' which was applied in order to prevent a crime and as a disciplinary measure,'' the Daily Mail quoted a law enforcement source in Tashkent as saying.

"Being surrounded by people from the Middle Asia, he was influenced by the recruiters who encouraged him to take part in fighting for terrorists in Syria.''

The source added: "Operational information is being collected and the family and friends of the family are being interviewed. The materials are being submitted to Russian colleagues.''

Asked by Uzbek police over his mother's role in the killing of a child, he disclosed her delicate mental state. "She was often bad-tempered, could start a scandal from nothing, broke dishes over things. But just a little bit later she behaved normally, as if nothing had happened.''