The powerful blast on the road connecting Srinagar and Jammu in India's Jammu-Kashmir state occurred when a Border Security Force convoy was passing by, said Neeraj Sharma, a spokesman for the paramilitary force.
The force is the main component of the Indian military fighting separatists in the region.
Kashmir's Inspector General of Police, K Ranjendra, told Aljazeera's correspondent six women and three children were among those killed.
"It was a massive blast followed by four more explosions," he said. He added the convoy was targeted while heading to Jammu, the winter capital of Kashmir.
The explosives had apparently been placed under a small bridge on a highway, added the correspondent.
Hizb al-Mujahidiin, the main group fighting Indian rule over the disputed region, has claimed responsibility for the attack, saying it was a "tribute to martyrs" who have died for the "Kashmiri freedom cause".
On 11 May, Indian forces gunned down a Hizb al-Mujahidiin divisional commander, Shakil Ahmad Bhat, also known as Khatib Ansari, on the outskirts of Srinagar.
The killing came less than a week after the group's Kashmir-based chief commander Abd Al-Rashid Shardar, also known as Gazi Shihab al-Din, died in a clash with the security forces, also in Srinagar.
The 15-year battle in the Muslim majority region has claimed more than 40,000 lives. However, local rights groups and separatists put the toll twice as high.
The attack came less than a day after Indian Prime Minister Manmohan Singh was sworn in as head of a new left-leaning government that has pledged to find a peaceful solution in Kashmir.