The Patna high court on Wednesday ordered serving of notice on former member of Parliament and Rashtriya Janata Dal candidate for the Madhepura Lok Sabha by-poll, Rajesh Ranjan alias Pappu Yadav, asking him to reply on October 6 why he re-entered Beur Jail in violation of rules once he had stepped out of it.

A division bench, comprising acting Chief Justice Nagendra Roy and Justice S N Hussain, ordered that the notice should be served through the Madhepura district magistrate, as the former MP is camping there to contest the by-poll.

Observing that the matter was "very serious", the bench said, if required, the Central Bureau of Investigation would be asked to conduct a thorough probe into the entire episode.

Yadav had re-entered Beur Jail on Sunday night in violation of the jail rules.

The court's order came after Inspector General of Prisons Deepak Kumar Singh submitted a report with regard to an alleged party hosted by Yadav for the jail inmates after the HC had granted him regular bail in connection with the murder of Communist Party of India-Marxist legislator Ajit Sarkar in Purnea in 1998.

The report, prepared after a visit by the IG Prisons and Director General of Police Narayan Mishra, confirmed that Yadav had re-entered the jail from Gate Number 1, but did not establish whether any feast had taken place.

The report said two sentries of Beur Jail who were posted at Gate Number 1 were suspended on the charge of dereliction of duty.