Calcutta: An employee of MP Birla Foundation Higher Secondary School was arrested late on Monday in connection with an alleged sexual assault on a three-year-old on the campus.

The arrest of Manoj - police have only identified him by his first name - followed a decision by the management of the Behala school to suspend him.

"Manoj has been arrested in connection with the assault case related to MP Birla school," additional commissioner (crime) Vishal Garg said on Monday night.

In the morning, many parents had gathered outside the school on James Long Sarani, in Behala, demanding the resignation of the principal and the vice-principal.

Manoj, a member of the cleaning staff of the school, was suspended after the agitation started.

"So far as we are aware, the investigation by the police into the alleged incident involving MP Birla Foundation Higher Secondary School has not come to any conclusion. However, today, after discussions with the police, a member of the service staff of the school has been suspended, pending inquiry/further investigation," a statement issued by the institution said.

The parents of the child who had allegedly been assaulted had lodged a complaint with Behala police station in September. Before that they had alerted the school about the alleged assault.

Earlier in the day, additional commissioner Garg said the police had "taken certain steps" following the complaint. "CCTV footage was seized and investigation is on." Asked about the parents' allegation of delay and inaction, he said: "I will not comment on that. You are free to interpret."

The parents of the alleged victim said in the afternoon the school had not taken any action on their complaint.

"An incident had happened in June and the authorities asked me to send my daughter to school with the assurance that there would be no more reason to complain. But there was a sexual assault again in September and the school authorities denied that any such incident had happened," the mother said.

The school's statement read: "In September 2017, the school received a complaint from a parent about acts of sexual misconduct against their child and immediately took various actions in that regard. The complaint did not specify any individual or particular person. The safety and well-being of the students being the uppermost concern of the school, immediate investigations were initiated into the complaint by the school management."

Around 6pm, the police allegedly lathicharged a section of parents who had blockaded buses leaving the campus with schoolchildren. "We had to push back those who were blocking the way so the students were not stranded," an officer said.

The agitating parents, however, claimed they had not stopped the buses from leaving. Some said teachers were leaving the campus in buses meant for students.

The teachers and the other employees were allowed to leave later in the evening.

The police in a Facebook post described the circumstances under which they had to "use force". One of the men protesting on the road had snatched the key from the driver of a school bus. Children in the buses were screaming "we are students of the school". Some of them started crying.

"At that moment the priority was to ensure safe passage of the students. Hence, we had to use force and engage in a scuffle," the post said.