Guwahati, Dec 25  : Two dreaded tribal separatists were killed Friday in Assam, bringing to four the number of militants gunned down since Thursday in the stepped up offensive against the outlawed National Democratic Front of Bodoland (NDFB).

A police spokesperson said a group of three armed NDFB militants challenged a security patrol early Friday near Rangapara in Sonitpur district, about 200 km north of here.

"The NDFB rebels opened fire at the security team and that led to the encounter in which two militants were killed. The third managed to escape under cover of the early morning fog," a senior police official said.

A large cache of weapons and explosives, including grenades, was recovered from the dead militants.

"The NDFB group was in the area for an extortion drive when security forces challenged them," the official said.

On Thursday, two NDFB rebels were killed in separate encounters with security forces in the same district.

"One of the two killed on Thursday was the prime suspect in the Bhimajuli massacre," the official said.

Twelve people were mowed down in a single attack at Bhimajuli in Sonitpur district in October, most of them Nepali speaking migrant settlers.

A massive security offensive was launched earlier this month against the NDFB in northern Assam after the outfit began an extortion drive in the area.(IANS)