Two of the injured persons are in the ICU of a private hospital in Imphal.
However one wounded victim said: "About eight tribals in combat fatigues climbed down from the nearby mountain and opened fire at us. Speaking tribal dialect, some of them mocked us and opened fire again."
Meanwhile, police investigation has not made any headway and no arrest has been made.
No underground organisation has claimed responsibility for the ambush.
Trucks, oil tankers and private vehicles ply on NH 37 under CRPF escort.
"Manipur had sought 60 companies of the central paramilitary personnel to escort the vehicles and gain area domination. However the centre has despatched just 29 companies," officials said.
Chief Minister Okram Ibobi Singh told IANS that from the very beginning, Manipur has been urging the central government to set up a highway protection force since NH 2 and 37 are the only lifelines of Manipur.
"However the centre maintains that as law and order is a state subject Manipur should deploy its forces along the highways," he said.
On Friday there was a total shutdown of markets, government offices, educational institutes and other facilities in protest against the ambush.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)