The victims were part of a special anti-insurgency force that was patrolling in Bishenpur district, about 45km southwest of state capital Imphal.

"The commandos were on a routine patrol when the convoy came under heavy gunfire with automatic weapons. The militants laid the ambush from atop a hill," police officer A. Singh told AFP by telephone from Imphal.

"The rebels were in an advantageous position and fired at the convoy indiscriminately for about 15 to 20 minutes, leaving no scope for retaliation."

Some 19 rebel groups are active in Manipur, which borders Myanmar, and their demands range from secession to autonomy.

More than 10,000 people have lost their lives to insurgency in the remote state during the past two decades.

The attack came a day after the state voted in the last stage of three-part assembly polls spread over two weeks, and in spite of heavy troop deployment.

At least 10 people, including three civilians, were killed by separatists during the elections.

The vote was one of a series of ongoing state polls seen as a reflection of the standing of the ruling Congress Party, which in Manipur had promised to tone down a tough anti-terror law and put more money towards development.

In response to the ambush, army and paramilitary troopers launched a massive hunt to track down the attackers.

"The terrain is hilly and probably the militants have by now moved out of the area to their bases," said another senior police official, asking not to be named.

No militant group claimed immediate responsibility for the ambush, which was laid in a stronghold of at least three separatist groups.

"The needle of suspicion is pointed towards the Kanglei Yawol Lanna Lup," said an intelligence official, who asked not to be named.

The group, founded in 1994, is fighting for an independent homeland for the majority Meitei community, who make up 70 percent of Manipur's population.

The militants have targeted security forces, drug dealers and smugglers, and have recently begun targeting teachers, in a bid to "cleanse" the state's education system.

Rebels have shot at the legs of teachers who missed class, police say.