They died when an improvised explosive device (IED) went off as a convoy of military vehicles drove on a highway some 20 kilometres (12 miles) from the main city of Srinagar.
"An IED went off as a CRPF (Central Reserve Police Force) convoy passed by," senior police officer Munir Ahmed Khan told AFP.
"We have 12 CRPF fatalities. We are evacuating the injured from the site and don't have their number at the moment."
The Press Trust of India (PTI) news agency put the death toll at 18.
Local media reports said the Pakistan-based Jaish-e-Mohammed Islamist group had claimed responsibility for the attack.
A spokesman for the group said "the suicide attack" was carried out by Aadil Ahmad, alias Waqas Commando, in a statement sent to local newspapers.
Unconfirmed photos showed the charred remains of at least one vehicle littered across the highway, alongside blue military buses.
It is the deadliest attack on Indian forces in that part of Kashmir since September 2016 when 19 soldiers were killed in a pre-dawn militant raid on the Uri army camp.
India has an estimated 500,000 soldiers in Kashmir, which has been divided between India and Pakistan and riven by unrest since the end of British rule in 1947.
Rebel groups have been fighting for an independent Kashmir, or a merger with Pakistan, since 1989.
New Delhi accuses Pakistan of fuelling the insurgency that has left tens of thousands of civilians dead.
Islamabad denies the charge, saying it only provides diplomatic support to Kashmiris' right to self-determination.