Officials say at least a dozen people have been killed after rebel gunmen opened fire at a market in the remote northeastern state. The region has long been prone to ethnic and tribal unrest.
Indian officials said attackers wearing military uniform opened fire at a busy market area just outside the town of Kokrajhar, 220 km (137 miles) west of Assam's main city of Guwahati.
They said at least 12 people were killed and 15 others injured in the attack, during which the attackers also threw grenades.
One assailant was killed, according to police, while the others are being pursued by security forces. Several homes and shops were said to have been badly damaged.
A senior official in the Indian capital, New Delhi, said initial reports suggested that separatist militants from the National Democratic Front of Bodoland were behind the attack. No claim of responsibility has yet been made.
The area, located near the border with Bhutan, is home to the indigenous Bodo people, who have been waging a violent campaign for their own homeland for decades.
Assam is one of India's most remote states, and suffers from severe underdevelopment. The nationalist party of Prime Minister Narendra Modi recently took power there in a state election.
tj/rc (AFP, AP, Reuters