Inspector General of Police AKM Shahidul Hoque and RAB spokesperson Mufti Mahmud Khan think militants are involved in the attack, carried out a day after raids on two militant hideouts in Chittagong's Sitakunda.

Airports, maritime ports and prisons across Bangladesh have been ordered to increase security following the attack.

Following a series of attacks on attacks and murders by suspected Islamist militants between early 2015 and mid-2016, the situation almost normalised amidst law-enforcing agencies' crackdown on militancy after the Gulshan and Sholakia terror attacks in July last year.

But the 'militants' broke the 'silence' through four incidents from Mar 6 to 11.

Middle East-based radical group Islamic State earlier claimed credit for several attacks, but this time, for the RAB camp attack, it has not issued any statement claiming its direct link to the assault. The IS mouthpiece only reported the attack.

And Bangladesh Police have not changed their statement that there is no existence of IS in the country.

How the attack happened

The construction of the new RAB headquarters in the compound started around three months ago. The compound has only one gate with a sign board ' Forces Barrack, RAB Forces Headquarters'.

A road of bricks has been set up inside the compound to facilitate the construction. Some blocks were seen piled at one side. Some cars were also seen on that side.

Besides some bachelor members of RAB's legal, media and communication wings, construction workers and supervisors stay in some tin-roofed buildings on the other side.

A washing area where personnel bathe and wash and hang their clothes is situated next to the buildings. Khan said at a briefing that the blast occurred at the washing area.

The attacker jumped over the boundary of the site for building the elite police unit's new headquarters around 1pm before the Juma prayers, said RAB spokesperson Khan.

"The unidentified intruder tried to escape when RAB personnel challenged him. That is when the explosion happened. He died when the bomb on his body exploded," he told reporters gathered outside the camp location.

He said workers and personnel were present at the site when the blast happened.

"Two of our personnel have been slightly injured. They are recovering at the Combined Military Hospital," said Khan.

The construction site for the RAB's new offices is enclosed by a boundary of grill and concrete, said Khan. It has an entrance which leads to a yard with few storage areas.

"Some of our administration officers stay here to look after the construction work."

Yellow police tape separated a section of that area, around 50 yards away from the entrance. An ambulance with tinted windows was seen leaving the camp around 2pm.

A RAB official said the attacker's spine and spareribs could be clearly seen on his chest and belly blew off in the blast. He said it seemed that he wore a suicide vest or belt.

Top RAB and police officials rushed to the camp after the attack that took place on the weekly holiday. Onlookers flocked outside the camp.

The chauffeur of a top RAB official said they heard a huge bang when the 'Khutba' was under way at the camp mosque before the Juma prayers. He said he came out to check the car and saw the blown off body of the attacker at the barrack.

Bashir Ahmed, who runs a tea-stall on the opposite side of the barrack, said he first thought a power transformer exploded when people were entering the mosque.

"Then I saw smoke rising from the barrack compound. I saw a body lying inside the compound through the gate," he said.

IGP Shahidul and RAB Director General Benazir Ahmed visited the camp in the afternoon. But they did not speak to the media there.

RAB bomb disposal teams swept the area to secure it. Nothing was found, officials said.

IS’ ‘Amaq News Agency Reports Suicide Bombing in Bangladeshi Capital https://t.co/TfQ3FUJd5x — SITE Intel Group (@siteintelgroup) March 17, 2017

'Militants did it'

Hours after the attack, the Islamic State's Amaq News reported the death of the suicide bomber inside the RAB camp.

The incident was reported in the Arabic and Bangla versions of Amaq.

It said a "camp for elite troops at the centre of the Bangladeshi capital" was targeted in a 'martyrdom operation' involving an explosive belt.

IGP Shahidul said the law enforcers were investigating the attack.

"We initially suspect that militants carried out the attack," he said.

He, however, stated that he did not know anything about the incident being mentioned in an Islamic State mouthpiece.

Earlier, RAB spokesperson Khan said, "We have not recovered any items from the man's body. Our priority is to secure the area and make sure if he was carrying anything else with him."

When asked whether they suspected any particular militant group, he said: "It cannot be confirmed immediately. But the nature of the attack indicates that the man was from an extremist group."

Writers, bloggers and publishers against extremism came under a series of deadly attacks from early 2015 to mid-2016. Policemen were also killed in attacks on check posts, and a suicide blast in a naval base mosque in Chittagong also took place at the time.

A week after the killings of 17 foreigners, two police officials and three other people in the Gulshan cafe attack on July 1 last year, the militants struck again through an attack besides the Sholakia Eid congregation ground just before the prayers.

The law enforcers killed some militant suspects in the crackdown after the July 2016 attacks. The law-enforcing agencies claimed the militants were 'weakened'.

But the four incidents this month hint at the regrouping of the militants.

The incidents are:

Mar 6: A prison van carrying death-row convict Harkat-ul-Jihad-al-Islami (HuJI) leader Mufti Hannan and his accomplices from court to the jail in Gazipur's Kashimpur came under attack in an attempt to snatch the militant leader.

Mar 7: Two suspected members of Neo-JMB were nabbed after launching an attack on policemen at a check post in Comilla. Police's counterterrorism unit took one of them to Chittagong's Mirsharai and busted a hideout. A large amount of bombs and explosives were recovered.

Mar 15: A militant couple were caught with explosives during a raid on a house at Amirabad in Chittagong's Sitakunda. Police raided another house in adjacent Premtala area following the information was given by the couple.

Mar 16: The 19-hour raid on the house at Premtala ended through an assault which saw the deaths of two militant suspects in a suicide blast and two others shot dead. A child also died in the explosion.

'A few militants always remain'

An official said Police Headquarters sent two letters relating to the warning and intelligence gathering to people concerned on Thursday.

The official, requesting anonymity, said the letters were sent to the deputy inspectors general of several ranges, and chiefs of RAB, SB, CID, PBI and other police units.

One of the letters carried instructions to heighten surveillance and alert level at sensitive places like mosques, temples, churches, and other significant government and non-government establishments.

The other letter asked to send information collected from field level on militancy, the official said.

The attack on the RAB camp took place within a day of issuing the letters.

Asked whether there was lax of alert due to calmness persisted for months, counterterrorism unit Additional Deputy Commissioner Sanwar Hossain said he did not think so.

"We work in our way. But the militants also try to make their presence felt. Today's incident was one of those," he said.

"There must be some elements here and there. If our drives cut off eight of the 10 hands, still two remain. They try to use those two hands. But our efforts always keep the threat level in check," he added.

He hoped the militants would lose the position to raise head because of the efforts of the law enforcers.

RAB's Khan thinks too that there is no lack in the security forces.

"Everyone is working. Many militants were nabbed or killed in drives by RAB and other agencies. Our job is to keep the threat level down," he said.