A four-year-old nursery student was allegedly sexually assaulted by the attendant of a school bus in Mumbai, India, police said on Friday.

The accused man, 35-year-old Ramesh Rajput, was arrested.

The alleged attack, the latest in a series of shocking crimes against women and children reported in India, happened when the children were being driven home on Tuesday afternoon.

The little girl, who attends one of the premier schools in the city, was the last child left on the bus to be driven home. The man allegedly forced the girl to move to the back of the bus and sexually assaulted her, NDTV reported, quoting police sources.

The man allegedly threatened the student with dire consequences if she revealed the incident to others. The child did not report the incident on Tuesday but confided it to her father the next day. The father reported the incident to the school authorities and lodged a police complaint.

"We have effected immediate arrest of the person concerned, registered a strong case for a non-bailable offence and will ensure that the culprit is punished severely. We will also terminate the contract with the bus owner," a trustee of the school was quoted as saying by the Times of India.

However, the police and the school authorities gave conflicting statements.

According to the police, there was no female attendant on board the bus during the crime. Regulations require a female attendant to be present on a school bus that carries female students.  

The school authorities refuted the police version. A statement by the school said that a female attendant had been present on the bus "at all times as per the guidelines of the school," and she "immediately confronted" the male attendant during the crime and "stopped" him. "The lady attendant was a supportive witness," the statement claimed, as reported by the Times of India.

The role of the bus driver was also under suspicion as he told the police that he had not known what had been happening behind him. He claimed that he had not heard the victim’s pleas for help.

The police said that they were inquiring into the lapses that possibly led to the offence, and they were also trying to find out if Rajput had committed a similar crime in the past.

The accused, charged under sections 376 (rape), 354 (molestation), 509 (insulting modesty) of the Indian Penal Code and under the Protection of Children from Sexual Offenses Act 2012, has been remanded in police custody until Feb 1.