Besides, two people were killed and over 20 injured in separate blasts, two at Bokajan area and one in the headquarter town of Diphu, yesterday.
This was the second massacre in the hill district during the past three days. Earlier, suspected militants had gunned down eight people of the Hindi-speaking community, including four women and three children, in the Bokoliaghat area on August 8.
Police suspected that yesterday's massacre was executed by the Karbi Longri Nationalist Liberation Front (KLNLF).
Karbi Anglong Additional Superintendent of Police (ASP) Nityananda Goswami said suspected KLNLF militants raided the Dolomora village near Shantipur, about 200 km from Bokajan police station, at 2145 hours yesterday.
The militants, armed with sophisticated weapons, barged into two houses and opened indiscriminate fire at 14 members of the two families.
The ASP said twelve people, including four women, died on the spot, while one person was admitted to the hospital in serious condition.
However, reports put the toll at 14.
The nearest police station, Bokajan, is about 200 km away and police could reach the site only this morning.
Karbi Anglong police chief Anurag Tankha said Army commandoes and paramilitary forces had been stationed in and around the area.
''Massive combing operations have been launched to nab the militants,'' he added.
Meanwhile, Chief Minister Tarun Gogoi was expected to visit the district this morning, official sources said adding that the chief minister would be addressing a public meeting at Bokolia where suspected ULFA and KLNLF militants massacred eight Hindi-speaking people on August 8.
Organisations of the Hindi-speaking community had called an indefinite National Highway blockade demanding the visit of the Chief Minister and Governor after the incident.
In January this year, over 80 Hindi-speaking people were killed in separate strikes by the ULFA in separate places at Upper Assam, mostly in Tinsukia and Dibrugarh.
Police suspected the massacres were part of the ritualistic terror campaign of the militants in the run-up to the Independence Day. A number of outfits of the North East, including ULFA, had already called for the ''ritualistic boycott'' of the Independence Day.