A five-member TMC delegation will visit Nagaland on Monday to stand by the families of those killed and injured in the firing incident in Mon district.

West Bengal Chief Minister and TMC supremo Mamata Banerjee has demanded a thorough investigation into the killing of civilians by security forces in Nagaland.

"This is to inform all that a five-member AITC delegation will be visiting Nagaland *tomorrow* to stand beside the families of those killed and injured in the heart-wrenching incident in Oting, Mon," the party said in a statement.

The delegation will comprise four MPs - Prasun Banerjee, Sushmita Dev, Aparupa Poddar and Santanu Sen - and party spokesperson Biswajit Deb.

Security forces opened fire on civilians killing 14 and injuring 11 more in Nagaland's Mon district in three consecutive incidents of firing the first of which was possibly a case of mistaken identity, police said on Sunday.

One soldier also died in rioting which followed.

The first firing which killed six civilians, occurred when army personnel mistook coal mine workers returning home in a pick-up van on Saturday evening, to be insurgents belonging to the Yung Aung faction of the banned outfit NSCN (K), about whose movements they had been tipped off.

As workers failed to reach their homes, local youth and villagers went in search of them and surrounded the army vehicles. In the ensuing melee, one soldier was killed and army vehicles burnt down. Soldiers who fired in self-defence killed another seven civilians, said, police officials.

At least one more person was killed and another two injured, as security forces fired at a group of people who attacked an Assam Rifles camp in the area, setting fire to parts of it.