Masked gunmen late Monday shot dead one of the sisters of Ranjan Daimary, chief of the outlawed National Democratic Front of Bodoland (NDFB), at her village home in Assam, officials said.
A police spokesperson said three to four gunmen attacked 40-year-old Lilawati Daimary at her residence at village Harisinga in Udalguri district, about 110 km north of in Guwahati.
Ranjan Daimary is believed to be somewhere in Bangladesh.
"Some three to four motorcycle borne gunmen with their faces covered by black cloth entered the house of Lilawati and shot her dead from close range using automatic weapons," a senior police official said.
Lilawati, a local schoolteacher and mother of four, was cooking in her kitchen when the attackers barged into their home and pumped bullets into her.
"Three to four bullets pierced her chest and forehead and she was dead on the spot," the official said.
The gunmen sped away in two motorcycles after the attack.
Lilawati's husband and their children were just a few metres away and were witness to the attack.
Lilawati is one of the two younger sisters of Ranjan Daimary.
The immediate provocation for the attack is not known, but security forces are not ruling out the possibility of the pro-talk NDFB faction being involved in the killing.
A bitter fratricidal war is on between the two rival NDFB factions.
The one headed by Daimary is opposed to holding peace talks and is operating out of bases in Bangladesh to carry out their hit-and-run guerrilla strikes.
The other NDFB faction led by guerrilla leader Gobinda Basumatary has entered into a ceasefire with New Delhi in 2005 and stays at designated camps run by the government.
On Sunday, two pro-talk NDFB rebels were killed in the western district of Kokrajhar with police blaming the Ranjan Daimary led faction as involved in the attack.
"We are not sure, but it could be the pro-talk NDFB that could have killed Ranjan Daimary's sister to avenge the deaths of two of their colleagues in Kokrajhar," the official said.
More than 100 people have lost their lives in fratricidal clashes between the two rival NDFB factions and also between the now disbanded Bodo Liberation Tigers and the pro-talk NDFB group.