Unidentified gunmen, suspected to be Kuki tribal militants, opened fire at oil tankers on Tuesday morning in Manipur's Kangpokpi district. The attack caused no casualty, the police said.

Some trucks and tankers coming from Assam towards Imphal were ambushed by the militants using automatic rifles. The personnel of CRPF escorting the convoy opened fire in retaliation. The exchange of fire took place at 5.45 a.m. along the National Highway No. 37, about 60 km from here, the police said.

Two tankers carrying petrol and diesel were hit by the militants' bullets.

Police units were rushed to the spot after the information about the ambush was received. However, the militants managed to escape.

The police officials suspect that it could be an extortion threat to the oil transporters.

"If the fuel had exploded on bullet impact there would have been casualties. We strongly condemn the attack," T. Kipgen, a resident said. Later, the trucks and oil tankers resumed journey towards Imphal.

"A few jeep-loads of CRPF personnel cannot ensure safety to over 600 vehicles along the mountain highway. We had welcomed the government's plan to deploy Indian Reserve Battalion (IRB) and police commandos along the vulnerable spots of the two national highways," Laishram Chinglien, a driver, said.

"However, the All Naga Students' Association Manipur (ANSAM) has strongly objected to it and the government cannot say or do anything," he added.

Officials said that the government plan has been staved off. In the past, police commandos and IRB personnel had to be recalled from Ukhrul and some other tribal dominated districts.

ANSAM and other Naga groups say that they object to the government plan to "militarise the lands of the Nagas".

The United Naga Council (UNC) had imposed an economic blockade for more than four months along the two highways which are the lifelines of Manipur.

The UNC was protesting the creation of seven new districts on the "lands of the Nagas" without consulting the stakeholders.

Chief Minister N. Biren Singh held a meeting with his cabinet colleagues on Tuesday morning to review the situation.

Official sources said that security along the highways would be beefed up, without which the drivers may refuse to ply. The IRB personnel and police commandos may be deployed shortly.