By Subir Bhaumik BBC correspondent in Calcutta

Separatist rebels have attacked a convoy of paramilitary troops in India's north-eastern state of Tripura, killing four soldiers and injuring at least 10 others.

Those killed belonged to the Tripura State Rifles (TSR), a special counter-insurgency unit raised by the state government to fight insurgents.

The outlawed National Liberation Front of Tripura (NLFT) says it carried out the attack, which came just before midnight.

The NLFT is one of several armed groups fighting for autonomy or independence from India in Tripura state.

Police officials told the BBC that a convoy of the TSR was heading back to their camp at Manu, in northern Tripura, when they were attacked by NLFT rebels.

'Vendetta'

The ambush was sprung near the village of Ghagracherra. Rebels fired from both sides of the hilly road along which the convoy was moving.

The rebels have targeted troops and Marxists

Four TSR personnel died on the spot, while 10 others, including a civilian driver, were injured.

Doctors say the condition of three of those injured is serious.

The rebels seized four automatic rifles from the TSR personnel.

An NLFT spokesman identifying himself as Major Yamrok called up newspaper offices on Thursday to claim responsibility for the attack.

He said the TSR troops had been torturing the local tribespeople to track down the rebels, and so, "needed to be taught a lesson".

Elections

Police say Yamrok is actually Shabir Debbarma, the NLFT's publicity secretary.

The NLFT has intensified its violent campaign in Tripura in the run-up to state assembly elections due early next year.

Supporters of the ruling Marxist party and security forces appear to have been their targets.

The Marxists allege that the NLFT is trying to ensure the victory of a regional coalition that they are accused of covertly supporting.

According to the ruling Marxists, this coalition has the support of India's National Congress Party as well.