Proper engineering effort had gone in digging the tunnel which shows the involvement of the establishment, BSF said in a statement.
A BSF team, probing the intrusion of four Jaish-e-Mohammed terrorists killed recently at Nagrota in Jammu, had gone 200 metres inside Pakistani territory to find the mouth of a cross-border underground tunnel used by extremists to enter into India, top officials said on Tuesday.
Immediately after the four Jaish terrorists were shot dead in a gunfight on November 19, the BSF, which mans the International Border in Jammu region, formed the crack team to explore the possible route taken by them.
The team followed its structure to unearth the opening of the tunnel on the Indian side and during the search operation, electronic and geographical data found on a mobile device recovered from the terrorists was also used, the officials said.
After detecting the mouth of the tunnel, the BSF team found itself 200 metres inside the Pakistani territory, they said, adding it entered through the tunnel and recorded the visuals inside it on the Pakistani side as part of collecting evidence, before they returned to the Indian side.
The operation was "swift and intelligence-based action", they said.
The four Kashmir-bound Pakistani terrorists were killed in the gunfight after the truck, in which they were travelling, was stopped for checking at Ban toll plaza on the highway.
The BSF, in an official statement, had said its personnel and those from the Jammu and Kashmir Police "detected a tunnel originating within Pakistan side of the International Border and exiting on the Indian side in the area of border post Regal in Jammu's Samba district".
"It was about 160 m from the IB, 70 m from the border fence and at a depth of 25 m," it had said.
Based on leads obtained after the encounter, the BSF had said, it was learnt that these terrorists "were picked up by a truck from Jatwal village in Samba on the national highway".
The tunnel, it had said, was found by the "first light" on November 22 by the BSF crack team. The exit on the Indian side was in thick bushes carefully concealed and meticulously covered with soil and wild growth.
"The mouth of the tunnel was strengthened and reinforced by sand bags with markings of Karachi, Pakistan," the border force that guards the front had said.
It was a freshly dug tunnel and appears to be used for the first time. It appears that proper engineering effort had gone in digging the tunnel which shows the hand of the establishment, the force said.
The nearest Pakistan posts are Chak Bhura, Rajab Sahid and Asif Sahid.
"The detection of the tunnel resulted due to the well-coordinated operation among the BSF, JK police and intelligence agencies," it had said.