NEW DELHI: The perpetrators of one of the deadliest attacks on the Army in recent decades that has left at least 18 soldiers dead are believed to have crossed back into Myanmar , with India contemplating all measures for retaliation, including assisting the neighbouring nation in flushing out the militants A day after the attack in Manipur ’s Chandel district, a massive operational and intelligence failure has come to light that led to the ambush of the Army administrative patrol in which soldiers could not effectively retaliate, boxed in by an IED blast and multiple rounds of rocket-propelled grenades.While officials are reluctant to share details, the Army is believed to be making detailed plans to bring the attackers to book, including the possibility of an operation by the crack para-regiment based on specific intelligence. Army Chief General Dalbir Singh is in Manipur to take stock of the situation while in Delhi, the Centre is planning to rope in the National Investigation Agency to probe the attack.By most accounts, the attackers — which the Army believes is a mixed group of Meitei militants led by the KYKL faction while internal agencies point to the Khaplang faction of the NSCN as the main player — managed to cross the international border into Myanmar by Thursday afternoon.Intelligence inputs with the Army suggest that the militant strike force of 15 heavily armed guerillas managed to reach a training camp at the Htan Ta Pin village in Myanmar which is barely 11 km away from the border town of Moreh. The detachment of militants that crossed over is believed to have been led by self-styled Lieutenant Tamba of the KYKL.While the militant group has been tracked crossing over, options are limited, given that the international border is a barrier for Indian operations. Myanmar’s help is being sought but the Army does not believe that much can be expected given that the neighbouring nation has little control over the border district and the area surrounding the town of Tamu where the village is located. Though joint operations have been carried out in past, the Army may have to go in on its own in case political clearance comes through.Even as investigations into the motive and composition of the militant group will be carried, an embarrassing operational and intelligence failure has come to light for the Army that has ordered a court of inquiry into the incident.Sources said that several standard operating procedures appear to have been violated, starting with the fact that the critical road opening party — tasked with clearing the route of the convoy — having failed to detect the presence of the militants. While the convoy — consisting of soldiers of the 6 Dogra Regiment proceeding on leave — was a soft target, the militants also managed to box in a leading vehicle the consisted of the elite ‘Ghatak’ quick reaction team of the regiment.Officials believe that the militants carried out the attack after over two weeks of preparation and deliberately chose a spot for the ambush that fell between the responsibility areas of the 20 Assam Rifles and the 6 Dogra Regiment.