Calcutta: The Airports Authority of India (AAI) is tightening its security regulations to prevent the entry of outsiders, including police, into air traffic control towers after Bengal cops twice breached the no-go zone of the city airport.

"We are preparing rules to ban the unauthorised entry of any outsider, including policemen, into the ATC towers, not only in Calcutta but across India. ATC towers are sacrosanct," Guruprasad Mohapatra, chairman of the AAI, told Metro on Tuesday.

"On two occasions, the police entered the ATC tower in Calcutta without permission. We had spoken to the state government after the first incident, but it happened a second time. We have to implement a rule (to prevent this)," he said.

On February 23, four policemen had entered the control room before the arrival of a flight from Bagdogra in Siliguri with chief minister Mamata Banerjee on board.

Three of the cops were allegedly not even carrying entry permits for the airport's high-security zone.

A replay on March 16 - two officers of the Bidhannagar police commissionerate sat beside the ATC in-charge for the entire duration of Mamata's flight from Bagdogra - led airport officials to question whether the police were empowered to enter the control room in the name of VVIP security.

The minister of state for civil aviation, Jayant Sinha, said during a daylong visit to Calcutta on Saturday that he would seek a report from the airport director and action would be taken, if necessary. "It doesn't matter who it is (behind the breach," he said.

The report reached the AAI's Delhi headquarters on Monday, sources said.

"The Central Industrial Security Force is the custodian of an airport and may seek the police's help for law-and-order issue, if needed. Only then can the police intervene," the AAI chief said.

According to him, entry passes issued to police personnel who are part of the security detail of VIPs and VVIPs do not entitle them to enter the air traffic control room.

An official said the report sent to Delhi mentions how two police officers from the Bidhannagar commissionerate entered the control room about 45 minutes before the chief minister's flight from Bagdogra on March 16 and stayed put till the plane landed.

"The duo told the ATC personnel that they were under instructions from high-ups to do so," the official said, quoting from the report.

In November 2016, the delayed landing of Mamata's flight from Patna and the pilot's statement later that the aircraft was running out of fuel had prompted the ruling Trinamul Congress to allege a conspiracy to murder the chief minister.