MOSCOW, February 29. /TASS/. A nanny has been arrested on suspicion of murdering a child thought to have been four-years-old, Investigative Committee regional official Yulia Ivanova said on Monday.

She was detained at a nearby subway station when the child's headless body was discovered after an apartment fire was put out in northwest Moscow.

"The child was found without the head. The nanny took the head away," Ivanova said.

"The woman waited till the parents and the elder child are gone and killed the toddler, setting the apartment on fire," the Investigative Committee said.

According to eye-witnesses, the woman dressed in black was carrying the head in her hands and was threatening to bomb the subway station.

A police source told TASS no explosives were found in her belongings.

The 39-year old woman, a national of a Central Asian country, will undergo psychiatric tests, police said.