In India's northeastern Tripura state, authorities say at least 20 paramilitary soldiers have been killed and five others wounded in an ambush by suspected separatist militants. India is battling several rebel groups in the remote northeast.

Police say the paramilitary soldiers were carrying two sick colleagues to a nearby town when their vehicle came under fire from armed militants hiding on a hilltop in the mountainous region, about 60 kilometers southeast of the Tripura's capital, Agartala.

Authorities say the militants triggered grenades, then opened fire with automatic weapons. Most of the soldiers died instantly, those wounded were taken to hospital.

Security forces are combing the jungles for the attackers, who escaped with arms and ammunition. Authorities say the attack was the biggest attack carried out by guerrillas in Tripura state in recent years.

Police officials are blaming the ambush on a banned tribal militant group called the National Liberation Front of Tripura. The group has been fighting for an independent tribal homeland for the last two decades. It also wants Bengali settlers in the area to leave, saying the indigenous culture of the tribals is being swamped by the Bengali immigrants.

Tripura's Chief Minister Manik Sarkar has blamed poor security along the Bangladesh border for the attack, saying militants are able to cross in and out of the state easily.

Tripura is one of seven states in India's remote northeast, a mountainous region that is home to more than 200 ethnic groups. The area is bordered by China, Myanmar and Bangladesh, and has been wracked by insurgencies for decades.

Most of the dozen rebel groups in the region complain of discrimination against the region's tribal population, and of neglect by the federal government. They want either independence or more political autonomy.