Three army personnel were injured in a freak accident in a practice drill ahead of Army Day parade, when soldiers displaying slithering operations fell from a helicopter following a malfunction in the craft's boom, to which the ropes were attached, officials said.

Army sources said investigation on how the accident occurred is in process.

Following the incident, display of slithering operations has been cancelled for the Army Day parade on January 15. The slithering operations, which involve troops slipping down a rope usually from a helicopter, is a method used to drop troops in an area of action when a chopper can not land.

The accident, a video of which has become viral on social media, occurred on January 9. Army sources said the 'boom' of the Dhruv Advance Light Helicopter (ALH), from which the slithering operation was being conducted, broke off.

The injury to the three soldiers is not "life threatening", and they are undergoing treatment.

Sources added that as a matter of protocol, all slithering operations from the ALH Dhruv will remain suspended till a probe in the incident is completed.

"The whole boom of the helicopter broke, it is likely to be some material-related issue, but the exact reason will be ascertained only after the inquiry report comes in," a source said.