Imphal, June 4: Militants firing rocket-propelled grenades ambushed an army convoy in Manipur this morning, killing at least 18 soldiers in what sources said was the deadliest single strike on the military wing anywhere in the country in nearly two decades.

The Nationalist Socialist Council of Nagaland (Khaplang), the Kanglei Yawol Kanna Lup (KYKL) and the Kangleipak Communist Party (KCP) claimed responsibility for the attack, some 30km from the Myanmar border in Chandel district.

The defence PRO in Guwahati put the toll at 18, while 11 soldiers were wounded. Police said a militant was also killed when the troopers of the 6 Dogra Regiment, made up mostly of personnel from Jammu and Kashmir and Punjab, fired back.

"The injured are undergoing treatment at the army hospital at Leimakhong, the army headquarters (12km from Imphal).... The casualty figure may go up," an Assam Rifles source said.

Seven of the injured have been admitted to the army base hospital in Guwahati.

The joint statement that claimed responsibility said a "combined team of elite strike unit of Naga Army, KYKL and KCP assaulted five-vehicle convoy of 6th Dogra regiment" and killed 20 personnel, including "one JCO" (junior commissioned officer.) The assault started around 6am and lasted till 9 to 10am, it added.

"The joint offensive has been launched in sync with each corresponding assertion for self-determination and sovereignty," the statement added.

In New Delhi, defence sources said this was the worst single attack on the army in nearly two decades. "Such ambushes were only heard of in Jammu and Kashmir in the mid-nineties," a source said.

Prime Minister Narendra Modi tweeted: "Today's mindless attack in Manipur is very distressing. I bow to each and every soldier who has sacrificed his life for the nation."

A spokesperson for the defence ministry said minister Manohar Parrikar had "assured that those who had committed this cowardly act would be brought to book".

Official sources said the militants ambushed the convoy at Moltuk, a hilly Kuki village nearly 118km south of Imphal, around 8am when it was on its way to the 26 Sector Assam Rifles headquarters at Pallel, 48km from the state capital. The first vehicle bore the brunt of the attack, the sources said.

Intelligence sources said the militants lying in wait in the surrounding hills used rocket-propelled grenades and opened fire from automatic weapons before the troopers of the Dogra Regiment, operating under 26 Sector Assam Rifles, retaliated.

The Khaplang group NSCN(K) and other militant outfits in Manipur, including the United National Liberation Front (UNLF), People's Liberation Army and the Meitei group KYKL have bases in neighbouring Myanmar.

The sources said the NSCN(K) could have entered the area recently after it abrogated the ceasefire with the Centre.