An Irish nanny has been remanded in custody in the US charged with murdering a one-year-old girl she was caring for, authorities have confirmed.

Aisling Brady McCarthy, 34, is also facing charges of assaulting Rehma Sabir on her first birthday, at the baby's home in Cambridge, Massachusetts earlier this year.

The nanny, who has been living in America illegally since 2002, had charges upgraded at Middlesex Superior Court today, the local District Attorney's office said.

She was refused bail and is due to appear in court again for a pre-trial hearing on 9 May.

Acting Middlesex District Attorney Michael Pelgro said the nanny is facing charges of first degree murder and assault and battery on a child causing bodily injury for allegedly violently injuring the baby, causing her death.

Court records previously revealed that a blood-stained pillow, blanket and baby wipes were found in Rehma's bedroom after emergency services were called to the home on Ash Street, Cambridge on 14 January.

The DA's office said a post mortem found that Rehma's death was caused by blunt force head injuries which were not accidental.

Records from today's arraignment hearing stated that Cambridge Police responded to a report of an unresponsive infant at the home and found baby Rehma breathing but unconscious.

She was taken to the Children's Hospital in Boston suffering from brain damage including subdural and retinal haemorrhaging and cerebral swelling.

The youngster was pronounced dead on 16 January.

Court records also stated that the police investigation, including witness statements, showed Ms Brady McCarthy, who had been living in the Quincy area south of Boston, was in sole care of Rehma on 14 January.

Police also alleged the nanny was the only person in contact with Rehma when she sustained abusive head trauma injuries that caused her death.

The Middlesex District Attorney's office noted that the charges against Ms Brady McCarthy are allegations and that she is presumed innocent until proven guilty.

Ms Brady McCarthy had been employed as a nanny by entrepreneur Sameer Sabir, the baby's father and his wife Nada Siddiqui, who is originally from Karachi, Pakistan.

The couple had moved from London to the US.

The nanny worked for them for six months up until their baby's death.