The explosion took place when an Army team was patrolling the Pallanwalla area.
A huge quantity of arms and ammunition including an AK assault rifle and a pistol were recovered from the intruder.
Singh had joined the Army in 2003 and was planning to take a leave to be with his wife who was expecting a baby anytime.
The firing from across the International Border (IB) in the Pragwal area of Akhnoor sector started in the wee hours, resulting in critical injuries to two BSF personnel manning a forward post, a senior officer of the border guarding force said.
The last terror attack took place on November 29, 2016 when terrorists wearing police uniforms attacked an army camp in Nagrota area of Jammu.
The GREF is the parent cadre force of the Border Roads Organisation (BRO) that builds and maintains border roads in the country.
Violating the ceasefire again, Pakistani troops opened fire from small arms along the Line of Control in Jammu and Kashmir's Akhnoor district.
Different sources told IANS in winter capital Jammu, "Pakistan Army violated the ceasefire on Friday, using small weapons and automatics".
Reports said mortars were also fired at the BSF posts and fell near civilian areas.
There have been 18 ceasefire violations along the Indo-Pak border in July in which four persons, including three jawans, were killed and 14 others injured.
The ceasefire violation on Wednesday was the seventh attack by Pakistani troops in July.
One woman was killed and six others, including two BSF jawans, were injured on Wednesday in a ceasefire violation in Akhnoor.
Congress on Wednesday condemned the ceasefire violation by Pakistan troops who resorted to mortar shelling in Akhnoor sector of Jammu district.
In fresh ceasefire violation ahead of the PM's visit in Jammu, Pakistani Rangers resorted to mortar shelling in Akhnoor sector of Jammu district.
Pakistani Rangers violated the ceasefire again and resorted to sniper firing, leaving a BSF jawan injured and triggering an exchange of fire in Jammu.
Congress leader Sham Lal Sharma said, "BJP has soft stand towards separatists and has joined hands with them to try political luck in Kashmir."
The tunnel was found at Munawar Tawi in Akhnoor. The police said there was no clarity over where the tunnel originated from.
All four injured belong to the Gorkha regiment of the Army.
<p>Forty-five pouches and 30 bottles of liquor, to be sold illegally, were seized in Jammu region's Akhnoor belt and two persons were arrested in this connection, police said on Sunday.</p>
There has been continuous firing since Thursday night by the Pakistani forces along the LoC at RS Pura, Akhnoor and Hiranagar sectors.
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