Three more persons were gunned down by NDFB rebels today to take the overnight toll in serial violence in seven districts of Assam to 21 as the authorities sounded a red alert across the State.

The rebels belonging to the anti-talk faction of the banned organisation shot dead two Hindi-speaking persons of a minority community at Ultapani in Kokrajhar district on the Indo-Bhutan border early this morning, police said.

Then in neighbouring Chirang district, the NDFB ultras gunned down a cycle mechanic at his residence at Domgaon village in the Bengtol police station area, they said.

In night-long violence yesterday, the rebels had killed 18 people, including eight Hindi-speaking and eight bus passengers, and injuring over 20.

Most of the attacks took place in Sonitpur district, bordering Arunachal Pradesh, where 14 people had been gunned down.