Indian police said on Monday that an explosion that killed six people and injured 32 in a packed cinema hall in northern India was a "terrorist" bombing.
Hundreds of people -- mainly poor migrant workers -- were crammed into the theatre in the industrial city of Ludhiana in Punjab state to watch Sunday's late-night screening of a new Bollywood comedy.
"It was a bomb blast. It is a terror act. We are trying to find out the exact nature of explosives used," said a senior police official on condition of anonymity.
Police have not named any suspect but a series of blasts across India in recent years have been blamed on Muslim extremists allegedly linked to Pakistan and Bangladesh.
India's 140 million Muslims celebrated Eid al-Fitr on Sunday, marking the end of the fasting month of Ramadan, and one of the biggest Islamic festivals.
Several of the wounded were fighting for their lives.
The Home Ministry in New Delhi said it was still "too early" to draw any conclusions.
Besides Islamic militancy, the Punjab was also the scene of a bloody Sikh insurgency in the 1980s.
Security at bus and railway stations and important buildings across the state was tightened, a Punjab police spokesman said.
India sounded a nationwide alert after that attack as the country prepares for the main Hindu festival season starting on October 21 with Dussehra which marks the triumph of good over evil.