Police in Russia have arrested a nanny who decapitated a child and took the severed head to Moscow metro station. The woman claimed to be an Islamic terrorist but police said she might suffer from mental issues.

Panic erupted outside the Oktyabrskoye Pole station in the north-west of the Russian capital, as the woman wearing a black full-body abaya robe pulled a head from a bag and started shouting Islamic slogans. A large number of police vehicles were deployed to the scene but didn't immediately intervene amid fears she might be wearing a suicide vest.

The station was shut down as police searched for possible explosive devices. The woman was eventually overpowered by a policeman, who could be seen tackling her to the ground alone before receiving back up by colleagues in footage uploaded online.

Authorities identified the suspect as a 39-year-old from Central Asia who worked as a nanny at a house that was set ablaze in the city earlier on 29 February. Rescue services responding to the fire found the decapitated body of a little girl at the premises.

A preliminary investigation concluded the nanny waited for the child's parents to leave before killing the girl and setting the apartment alight. "The child was found without the head. The nurse took the head away," said Yulia Ivanova, an official with Russia's federal police authority, the Investigative Committee, Tass news agency reported.

Video images from outside the metro station showed the woman holding the head in one hand, while waving the other in the air and shouting slogans. She reportedly yelled "Allahu Akbar" and "I am a terrorist" as she walked up and down a sidewalk facing the metro's entrance.

Local media identified the victim only as Nastya M, aged three or four, and said the mother has been taken to a hospital after falling ill. Russia's Children's Rights Commissioner, Pavel Astakhov, tweeted: "Before hiring a baby-sitter for your child at least make sure of her mental state". No explosives were found on the woman or at the station.