A Jeep full of explosives rammed a convoy of Indian paramilitary police in Kashmir, killing more than 44, with many others injured.
The Inspector General of India's Central Reserve Police Force, Zulfiwar Hassan, visited the site of the blast and declared it to be a "terror incident".
An Islamist group Janish-e-Mohammad with ties to Al Qaeda and the Pakistani Taliban has claimed responsibility.
The territory bordering India and Pakistan has been the subject of a large and militiarised territorial dispute for decades, with this latest attack being the deadliest in 20 years. India has about half a million troops currently stationed in Kashmir.
While border skirmishes are common, this attack was located about 20km from the capital Srinagar.
This latest incident is expected to stoke unrest among the area's majority Muslim population. Indian's Information Ministry issued a warning to broadcasters not to show any content that promotes anti-national attitudes.