Top police officials of different units have been instructed to remain alert as police suspect extremists' links to the explosion in the capital's Paltan and the bomb-like substance recovered in Gulistan in the last two days.
Friday night's explosion at Paltan intersection resulted in no casualties. A bomb-like object was recovered in Gulistan the following night.
At least three district superintendents of police (SP) and chiefs of two different units confirmed to The Business Standard that they had been asked to remain alert ahead of Eid-ul-Adha.
On July 19, police headquarters issued a letter regarding a possible attack by members of the so-called Islamic State just ahead of Eid in the name of their so-called mission "Bengal Uliyah" or "Bengal Khilafat," and alerted all the district SPs and other respective units.
In the letter, three embassies, international airports, Ahmadiyya/Shia community mosques, temples, pagodas, churches, policemen, police vehicles, and police infrastructure were mentioned as the possible targets of militants.
An official of the diplomatic security division of Dhaka Metropolitan Police (DMP) told The Business Standard that they had been instructed to deploy more forces at three embassies.
"We suggested our members not move alone, and also instructed them not to keep vehicles parked without someone present," he added.
Ashraful Islam, deputy commissioner of the division, said they were instructed to remain alert.
A deputy commissioner of Chattogram Metropolitan Police also confirmed that they had been instructed to be alert for such attacks in the port city.
The letter issued by the police headquarters described possible attackers as anonymous bearded persons aged 15-30, and suggested unit members be careful about people with such appearance.
The time slots of 6am-8am and 7pm-10pm were mentioned as the possible time of an attack.
"Militants might also come to police stations or offices wearing police uniforms. So, be careful about anonymous uniformed policemen. Search them and quiz them," the letter read.
Meanwhile, Enamul Haque Mithu, additional deputy commissioner of DMP Motijheel zone, said a case was filed with Paltan Police Station in connection with Friday's explosion.
He said police were yet to decide on filing a case over recovery of the bomb-like substance, which later turned out to be fake.
Mithu said the counterterrorism unit is likely to take charge of the investigations in the coming days as these incidents may have extremist links.
The incidents took place a few days after DMP Commissioner Shafiqul Islam had warned that police might be targeted for extremist attacks.
The DMP bomb disposal unit's Additional Deputy Commissioner Rahmat Ullah Chowdhury told The Business Standard that they had visited the spots, and recovered explosives and objects on both occasions.
The devices used to make bombs that exploded on Friday night were similar to those used to make improvised explosive devices that have been used to attack police before, he said.
"They were also controlled far away from the scene like remote-controlled explosives," Rahmat said.
He suspected that a cell of Neo JMB might be involved in the attack because the patterns for making the explosives and devices used were similar.
Police were repeatedly targeted for extremist attacks, and at least five such attacks occurred last year.
Serial attacks on police in the capital began on April 29 last year and by August 31, five such attacks were made, according to media reports.
Five policemen, a community police member, a rickshaw puller, and a woman were injured in blasts in three of the five attacks.
During the attacks, bombs went off in Gulistan, Malibagh and at the Science Lab intersection. Two bombs were placed in Khamarbari, but they were recovered before they could be detonated.