Some 2,500 soldiers were in different buses on a sanitized and heavily-protected highway when the blast took place at Awantipora, around 20 km from Srinagar. Officials said an unusually high number of personnel were on the move at the same time because the Srinagar-Jammu highway had been shut for the past two days because of bad weather.

The convoy reportedly left Jammu around 3.30 a.m. this morning. The suicide attacker, driving towards the convoy from the opposite direction, rammed a bus with 39 personnel. The massive blast left human remains and wreckage scattered on a 100 metre stretch of the highway, slick with snow.

The bus that was targeted was reduced to mangled metal. Several other vehicles in the convoy were also destroyed.

Claiming the attack, the Jaish e Mohammad put out a video and photos of an armed man it claimed was the suicide attacker -- Adil Ahmad Dar or Waqas Commando from Kakapora in Pulwama. Adil Ahmad joined the Jaish e Mohammad last year.

Sources said Jaish-e-Mohammad had warned of a suicide attack in Kashmir just two days ago, and added that the Criminal Investigation Department of the state police had shared the video and input about the possible attack with intelligence agencies.

Bullet marks on the bus indicate that more terrorists may have been hiding and may have fired at the convoy. "It's a terror incident, we are looking into what caused it. We suspect it was a vehicle-bound attack," a top CRPF officer told reporters.

Asked how the attackers could carry out the explosion on such a heavily-guarded highway, the CRPF said, "It is a matter of investigation".

Union Minister VK Singh tweeted: "As a soldier and a citizen of India, my blood boils at the spineless and cowardly attacks. 18 brave hearts from the @crpfindia laid down their lives in #Pulwama. I salute their selfless sacrifice & promise that every drop of our soldier's blood will be avenged. #JaiHind"

This is the biggest attack on security personnel in Jammu and Kashmir in decades. In 2001, three terrorists of the Jaish-e-Mohammad attacked the Jammu and Kashmir state assembly in Srinagar using a Tata Sumo loaded with explosives. 38 people were killed. In 2016, India retaliated sharply after four heavily armed terrorists targeted an army brigade headquarters in Uri -- causing over 19 deaths. The Indian army carried out a cross-border surgical strike in which several enemy installations were reportedly destroyed.