In a daring highway robbery, three unidentified persons looted Rs 21 lakh in cash from an Automatic Teller Machine (ATM) of a bank on the outskirts of Tumakuru town in southern Karnataka, said police on Tuesday.

"The loot took place in the wee hours of the day when the accused trio assaulted and tied up security guard Gangappa, 55, with ropes and decamped with the cash worth Rs 21 lakh in Rs 2,000, Rs 500 and Rs 100 notes from the ATM," Tumakuru Deputy Superintendant of Police Chidananda Swamy told IANS.

The ATM of the state-run Karnataka Bank Ltd is located at Gubbi on the ring road, connecting the town to the state highway, about 80 km from Bengaluru.

"We have registered an FIR (First Information Report) under section 392 of the IPC (Indian Penal Code) on a complaint by the security agency CMS (Cash Management Service) and the bank and launched a manhunt to nab the culprits," said Swamy.

According to the guard, the trio entered the ATM kiosk, pulled down its shutter, disconnected the CCTV camera and withdrew the entire cash from the machine by using a duplicate key and passwords as they were familiar with its operation.

"From the video footage we have till the trio entered the kiosk and shut the camera, it appears to be a handiwork of the agency's staff as the guard had seen two of them visiting the ATM to fill cash on earlier occasions," said Swamy quoting the guard.

The district police have set up a special team to investigate the heist and stepped up vigil at check-posts in the district to trace the suspects.

"The ATM has been found intact, with no sign of attempts to break it open or tamper with its cash box. The accused appears to be familiar with how it works," added Swamy.