Guwahati, Nov 9 (IANS) Assam's fragile peace was shattered Monday when tribal separatists killed at least 18 Hindi-speaking people, including eight bus passengers, in three separate attacks in the northeastern state of Assam, officials said.

Eight people were also injured in the attacks.

A police spokesperson said heavily armed militants of the outlawed National Democratic Front of Bodoland (NDFB) fired at a bus near Bhoimari village in Sonitpur district, about 250 km north of Assam's main city of Guwahati. They lined up the passengers and took away the Hindi-speaking people to the forest and shot them.

"The NDFB fired at the bus, forcing the driver to stop, after which the militants lined up all the passengers on the road and took away at least 10 of them at gunpoint," a senior police official said.

There were about 25 people on board the private bus carrying Arunachal Pradesh government employees.

Police later recovered the bodies of eight people from a thickly wooded area close to the place where the bus was stopped.

"All the dead were Hindi-speaking people hailing from Bihar and were Arunachal Pradesh government employees," Assam police chief Shankar Baruah told IANS.

The whereabouts of two other passengers were not known. Police, army, and paramilitary troopers have launched a massive hunt in the area.

In another incident around 6 p.m., five people, including a woman, were killed after NDFB militants opened indiscriminate fire near village Belseri in Sonitpur district.

"All the victims were Hindi-speaking people," a police official said.

In the third attack, a daily wage earner, also a Hindi-speaking person, was killed in Tamulpur area in Nalbari district in western Assam.

Police blamed the attacks on the NDFB, a rebel group fighting for a separate homeland for the Bodo tribals, with their unique culture and ethnicity. There are approximately three million Bodos in Assam's 26 million population.

"We condemn the barbaric attack on innocent civilians by the NDFB and I assure you of very tough security measures against the rebels," Chief Minister Tarun Gogoi told IANS.

The incident comes hours after security forces Monday morning gunned down a NDFB militant in Sonitpur district during an encounter.

On Nov 1, the NDFB threatened to kill 20 or more people if one of their cadres was killed by security forces in any encounter.

"From today onwards, if any innocent NDFB cadres are killed by Indian forces in the name of fake encounter then the Boroland Army (armed wing of the NDFB) would take action against any Indian," deputy chief of the Boroland Army, B. Jwngkhang, said in an emailed statement Nov 1.

"One innocent Boro would be equal to 20 Indian or may be more and we don't care who they are, maybe Indian civilians or Indian forces."

Security forces in the past three months killed at least 20 NDFB cadres, besides arresting more than 15 militants in separate raids even as the tribal separatist group continued with a series of kidnappings for money.

"And this (threat) would be anytime and any moment and we are ready to strike. Remember this warning and be serious before killing any innocent Boro people," the rebel statement warned the Assam government.