All 18 fatalities were parliamentary police, with the explosion heard from several miles away. The Indian-ruled part of Kashmir has been plagued by violence for years, with clashes between security forces and militants killing more than 100 civilians over the past year. Islamist group Jaish-e-Mohammad (JeM) took responsibility for the attack, according to local news agency GNS.
Mohammad Yunis, a journalist who reached the site minutes after the explosion, told Reuters he saw blood and body parts scattered along a 100-metre stretch on the highway.
Kashmir's Police Chief S.P. Pani said the Central Reserve Police Force had suffered major damage.
He said: "It is a terror incident and we are looking into the possibility of what led to the blast. We are going to go for post blast investigation.”
At least 12 students were injured in an explosion at a school in Kashmir on Wednesday, police said, though the cause of the blast was not immediately clear.