New Delhi, June 4 (IANS): On a day when at least 20 soldiers were killed by militants in Manipur, defence expert and former Indian Army officer Brig. S.N. Chatterji (retd) said the incident indicates external interference in the northeast was on the rise.

Certain areas in the northeast have been on the boil for a while.

On April 2, three Army personnel were killed in an ambush by NSCN-K in Tirap district in Arunachal Pradesh. On May 3, seven Assam Rifles troopers and one personnel of the Territorial Army were killed in another ambush in Mon district in Nagaland by joint forces of newly floated United Liberation Front of Western South East Asia comprising NSCN-K, ULFA, Kamatapur Liberation Organization and NDFB-Songbijit.

"There are reports that a month and a half back, leaders of these insurgent groups travelled to China," Brig. Chatterji told IANS.

"It is possible that there are external factors responsible for the recent spurt in incidents.

"It can be a desperate step to disturb peace, specially since the new government has been firm on the boundary issue," he added.

At least 20 soldiers were killed and 11 injured on Thursday when militants ambushed their convoy in Manipur's Chandel district.