KOLKATA: The man who sneaked past security guards and entered the premises of Chief Minister Mamata Banerjee's residence in the city has told the police that he had done so thinking it was the Kolkata Police headquarters, a senior police official said on Monday.

Hafizul Mollah, who is in his early 30s and from Hashnabad in West Bengal's North 24 Parganas district, could not, however, clearly state why he needed to go to the Kolkata Police headquarters in the dead of the night, he said.

The man had scaled a boundary wall of Banerjee's private residence at 34B Harish Chatterjee Street in Kalighat area of the city at around 1.20 am on Sunday and remained there till morning.

The security personnel posted there spotted him at around 8 am on Monday and handed him over to officers of Kalighat police station.

"During initial grilling the man said he mistook the CM's residence to be Lalbazar Kolkata Police headquarters and entered the premises. But he could not give any proper reply when asked about why he wanted to go to the police headquarters at that hour," the police official told PTI.

Mollah during grilling had first claimed to be a fruit seller and then a "good" vehicle driver, he said.

Police said that going by the man's appearance he seemed to be "somewhat mentally unstable".

The investigating officers are drawing a map as per his descriptions about his activities throughout Sunday before reaching Kalighat.

"We are verifying his claims. Our officers are trying to draw a picture of his activities throughout Sunday and when and how he arrived at Kalighat. Also to find out whether he was alone or was he accompanied by anyone, how he managed to go past the security personnel and enter the CM's premises without being caught," the police official said.

Police have booked Mollah under IPC section 458 and sent him to police custody till July 11.

The IPC 458 deals with lurking, trespass or house-breaking by night after preparation for hurt, assault or wrongful restraint.

Senior administrative officers met at the state secretariat on Monday and reviewed Banerjee's security arrangements.

The incident triggered a security scare and questions were raised about how the man went past the Z-Plus security cover that Banerjee gets and entered her private residential premises located in the 'high secure' neighbourhood to spend a night there without anyone noticing him.

Police have taken immediate steps to enhance security in and around the CM's residence, the official said.