The Army on Sunday said the investigation into the "sad and unfortunate" loss of lives in the December 4 firing incident in Mon district of Nagaland is progressing expeditiously and all efforts are underway to conclude the probe at the earliest.

The Army also assured that action would be taken in the case in accordance with the law to "secure justice for all" and urged the people of the state "to be patient and wait for the findings of the Army inquiry".

Fourteen civilians were killed in the botched counter-insurgency operation that had triggered massive public outcry in Nagaland and a demand to lift the Armed Forces (Special Powers) Act.

Following the incident, the Army ordered a Court of Inquiry headed by a major general posted in the northeastern region.

"Indian Army wishes a happy new year to the people of Nagaland and we pray for the good health, peace, happiness and prosperity for the people. We once again deeply regret the loss of lives during the December 4 incident in Mon district. Loss of lives is indeed sad and unfortunate," the Army said in a statement.

It said the inquiry ordered by the Army is progressing expeditiously and all efforts are being made to conclude it at the earliest.

"We have taken out notices for people to come forward and assist us in the inquiry by providing any information including videos, photos or any other material from original sources and will be grateful for the same," it said.

"This can be conveyed on Whatsapp Messenger at +916026930283 or Army Exchange Helpline +913742388456," it added.

It said the Indian Army is also fully cooperating with the probe by the special investigation team (SIT) ordered by the state government and required details are being shared in a timely manner.

"We request all brothers and sisters of Nagaland to be patient and wait for the findings of the Army inquiry. We assure you that action will be taken in accordance with the law to secure justice for all," the Army said.

It said the people of Nagaland have always cooperated and assisted the security forces in maintaining peace and tranquillity over the last many decades.

"We share a deep bond of brotherhood, trust and friendship with you. Let us work together for a brighter and better future," the Army said.

Meanwhile, the Centre has decided to set up a high-level committee to examine the possibility of lifting the controversial AFSPA in the northeastern state where it has been operational for decades, according to officials.

The AFSPA empowers security forces to conduct operations and arrest anyone without any prior warrant. It also gives immunity to the forces if they shoot someone dead.

The decision to constitute a high-level committee was taken at a meeting chaired by Union Home Minister Amit Shah and attended by chief ministers of Nagaland and Assam Neiphiu Rio and Himanta Biswa Sarma respectively on December 23, an official said.