Controversial Uttar Pradesh Minister Raghuraj Pratap Singh alias 'Raja Bhaiya' resigned today and faced possible arrest after he was booked for alleged conspiracy in the killing of a police officer over which a CBI probe will be ordered.

Facing heat over the alleged involvement of Raja Bhaiya in the murder of DSP Zia-ul-Haq in mob violence in Pratapgarh district on Saturday, Chief Minister Akhilesh Yadav rushed to the officer's native village in Deoria and assured his wife Parveen Azad her demand for a CBI inquiry would be accepted.

"Action will be taken. Anybody who is accused no matter how big the person is he will be sent to jail. A CBI probe will be ordered," Akhilesh told reporters after his visit that was marked by shouting of anti-government slogans. Two persons including Raja Bhaiya's supporter Guddu Singh have already been held after four FIRs were filed in the case.

Akhilesh earlier told the state Assembly, which was rocked by the killing, that a "just and impartial" action would be taken against those responsible.

44-year-old Raja Bhaiya, who has a criminal record and has been jailed before, figures in the FIR filed by the slain officer's wife Parveen Azad in which the minister was accused of criminal conspiracy. Parveen also demanded a CBI probe.

A five-time Independent MLA from Kunda and a Food and Civil Supplies minister, he met the Chief Minister in Lucknow and submitted his resignation, official sources said, adding the resignation has been accepted by Governor B L Joshi.

Zia, posted as Circle Officer at Kunda town, was killed by a mob in Pratapgarh on Saturday when he had rushed there during the course of his duty after a village head was shot dead over a land dispute.

Pleading innocence, he rejected the charge that he had an old score to settle with Zia. "Had I been so opposed to the CO I would have easily got him transferred instead of getting him murdered", he added.

Shortly after he resigned, Raja Bhaiya made a statement in the Assembly demanding a CBI inquiry and reiterated he was ready to go to jail to save embarrassment to the Samajwadi Party government.

Eight policemen including the Inspector at Kunda police station in Pratpgarh district were also suspended for fleeing the spot when the DSP was being attacked.