The deaths occurred when Indian troops Thursday launched a raid on a hideout of the outlawed People's Liberation Army (PLA) in the Thangjing hills, about 70km south of Manipur's state capital Imphal, a police spokesman said.

"Five army soldiers and four PLA rebels have so far died in the encounter," the police spokesman said by telephone from Imphal, requesting anonymity.

The PLA is a rebel group fighting for an independent homeland for the majority Metei community in Manipur, bordering Myanmar.

"The operations are continuing Friday and according to our reports some more militants were killed though we are yet to get details as the location is very remote and inaccessible," army spokesman Lieutenant Colonel Santanu Dev Goswami told AFP.

"The militants were involved in a massive extortion drive in the area and hence the military operation."

Goswami said a huge cache of arms and ammunition, including AK-47 assault rifles, rocket launchers, grenades and radio sets were recovered from the slain rebels.

An ongoing military offensive by the Indian army has been under way since October against three frontline militant groups in Manipur, in which some 7,500 army troops are involved.