The GREF is the parent cadre force of the Border Roads Organisation (BRO) that builds and maintains border roads in the country.
Sources said two to three attackers launched an assault on the camp around 1 am in Jourian area, 55km from Jammu, near the border with Pakistan.
The army cordoned off the camp and launched an operation against the gunmen after this year’s first attack in the Jammu region.
The militants likely infiltrated from across the border to carry out the attack, sources said.
The militancy-hit state of Jammu and Kashmir saw heightened tensions in 2016.
In the last week of November, seven soldiers, including two Majors, were killed when militants dressed as policemen stormed a military camp in Jammu’s Nagrota.
The brazen attack was the second in as many months since the siege of another army base at northern Kashmir’s Uri left 19 Indian soldiers dead, spiking tensions between India and Pakistan.
The border areas also saw repeated ceasefire violations by the neighbour, with both India and Pakistan citing civilian casualties in cross-border firing.