The force later examined the tunnel and found plastic sandbags on its mouth that had “Pakistani markings” on them, officials told PTI.
A senior official said BSF troops got suspicious after noticing the sinking of earth at some places due to recent incessant rains.
An earth moving machine was immediately pressed into service to completely unearth the tunnel, the official said, adding the spot inspection revealed that the tunnel was under-construction and about 20 metres long.
The tunnel, as per sources, has a depth of about 25 feet at the opening and has been located near the ‘whaleback’ border post of the BSF.
The force has launched a mega search operation along the IB in this area to detect any other such clandestine structure.
BSF Inspector General (Jammu) N S Jamwal also visited the spot to oversee the operation, they said.
About 8-10 plastic sandbags that have ‘Karachi and Shakargarh’ written on them have been recovered from the opening of the tunnel and the bags have a manufacturing and expiry date embossed on them indicating they have been manufactured recently, officials said.
The nearest Pakistani border post ‘Gulzar’ is about 700 meters from the tunnel, they said.