Sylhet: Bangladesh Army on Tuesday wrapped up their assaults on the militant den in Sylhet that killed all four extremists, one being the presumed chief of Neo-JMB, while the outfit's retaliation saw deaths of six including two police officers near the scene.

"Accomplishing all (our army) actions, the building has been handed over to the police administration as a 'crime scene' this afternoon with announcement of the end of Operations Twilight," army spokesman Brigadier General Fakhrul Ahsan told a news briefing at Jalalabad Cantonment.

He added that the army commandos main assault, however, was ended yesterday with deaths of all the four militants inside Atia Mahal but it took military one more day to accomplish the required procedures including further security searches and disposal of devices left by the slain extremists.

Ahsan, the director of army intelligence, also said suicidal vests worn by the last two slain militants were also defused through controlled explosion inside the building "in the interest of security and requests from police administration".

He said the operation prioritized safe evacuation of all ordinary residents of the five-storey building having 30 flats and added all the 78 of them, including 21 children, were moved out safely as the salvage campaign was carried out from the rooftop, placing roof-to-roof ladders from an adjacent building. 

Commander of army's Sylhet-based 17th infantry Division, having a specialized commando unit, Major General Anwarul Momen led the operation which was joined by another specialized military team after being flown from Dhaka by helicopters.

"Operation Twilight will remain as a milestone of cooperation between military and civil administration in facing any crisis in the country," he said adding the entire operation was carried out in line with Prime Minister Sheikh Hasina's specific directives.

The building was under security siege for the past five days while the army was called out on Saturday morning.

The military briefing came hours after police suspected one of the four militants killed in the army assault in Sylhet to be Musa, the chief of Neo-Jamaatul Mujahideen Bangladesh (neo-JMB), which staged the deadly July 1, 2016 attack on a Dhaka caf,. 

"Our intelligence suggests one of the four is top neo-JMB leader Musa," police's assistant inspector general M Moniruzzaman told BSS but added that forensic investigation, however, was ordered to confirm his identity as his face was mutilated in the security encounter. 

Officials earlier identified the man only as Musa saying he took charge of the outfit as a massive anti-militancy clampdowns killed several top neo-JMB leaders after the July 1, 2016 attack on the Holey Artisan restaurant that saw deaths of 22 people, 17 of them being foreigners on that night.

Army commandos subsequently shot dead six extremists at the scene next morning. 

The Operation Twilight was wrapped up hours after explosions rocked the neighbourhood as army troops cleared the wired militant den. 

Witnesses and officials said smokes rolled upward after several powerful blasts rocked the area as army's bomb disposal experts were engaged in defusing the explosives laid out at different corners of the building by the militants before their deaths. 

An official familiar with the operation said they army troops used a drone to get a clearer picture before stepping inside different corners of the building to evade "booby traps". 

Of the four slain militants, a male and a female militant were killed yesterday a day after the two others detonated their suicide vests after being shot by para-commandos. 

Security officials suspected Musa was killed in the yesterday's assault along with the female, while the other two had detonated their suicide vests after being shot by para-commandos on Sunday. 

In the evening of the same day fellow extremists from outside, visibly being mixed up with onlookers, launched a retaliatory attack killing six people, two being police officers near the building as the commandos prepared for their final assault. 

The militants staged two subsequent blasts within an hour at the site that wounded two army officers serving the elite anti-crime Rapid Action Battalion (RAB) and nearly 50 onlookers who were watching military actions from a safe distance. 

According to US-based Site Intelligence, Islamic State claimed the responsibility, which Home Minister Asaduzzaman Khan Kamal immediately called unfounded, attributing the attacks to homegrown militants. 

Ahsan yesterday told the media briefing powerful "improvised explosive devices" or IEDs laid by "much trained militants" at its different corners exposed the building to vulnerability requiring the military to exhaust a process ahead of wrapping up the operation. 

"The militants had kept a bucket filled with explosives at the collapsible gate at entrance of the building. When we detonated them from distance, the collapsible gate was blown out so vigorously, walls of another building several yards away were severely damaged," Ahsan said describing the strength of explosives used by the militants. 

He earlier also described the militants as "well trained" referring to an example when they hurled back a live grenade thrown by the commandos as the assault was underway. 

The military commandos were called out to neutralize the extremists after two days of siege enforced by police's SWAT, counter terrorism unit, fire service and RAB that draws personnel from police and military forces. 

Residents who lived in the house as tenants said they were virtually taken to hostage with militants warning them of bombs implanted on their way out while the commandos brought them out from the top of the building making their way there from the rooftop of an adjacent structure.

Police had tracked down the Sylhet hideout less than a week after they busted two militant dens on the outskirts of southeastern port city Chittagong, where four Islamists were killed.