DHAKA: At least one person was killed and nearly 80 wounded Saturday in a bomb attack near the main imabargah in the Bangladeshi capital as thousands gathered for the annual Ashura procession, police said.

Police said it was believed to be first time Bangladesh's Shia community has been targeted and came just weeks after an Italian aid worker and a Japanese farmer were shot dead in attacks claimed by the self-styled Islamic State (IS) group.

Officers said a 14-year-old boy died on the spot after three small bombs were thrown at the complex of the Hussaini Dalan, the main imambargah in the old Mughal quarter of Dhaka, at about 2:00 am Saturday.

"There were some 20,000 people in and outside the building at that time. They were preparing to hold the annual Muharram mourning procession when the three (bombs) were exploded," deputy commissioner of Dhaka Police Mofiz Uddin Ahmed told AFP.

Local police chief Azizul Haq said at least one person was killed and around 80 injured in the attack, which took place on the premises of the 17th century religious site.

"We've recovered two unexploded bombs. These are like explosive devices and almost like grenades and fitted with batteries," Haq told AFP, adding one person had been detained.

Police inspector Mozammel Hoque told AFP that most of the injured were hit by bomb splinters but no-one was in critical condition.

"Some 50 were brought to the Dhaka Medical College Hospital. A 14-year-old boy was brought in dead. He died due to the explosion," he said.

In Bangladesh, television showed live footage of the chaos in the aftermath of the blasts with people, many holding flags, fleeing and ambulances taking the injured to hospital.

Witnesses told the mass-circulation daily Prothom Alo that many mourners fell to the ground as loud explosions went off just at the main gate of the Hussaini Dalan, the most important prayer and congregation site for Bangladesh's Shias.

Roni, who uses one name, said mourners in black were holding prayers just before the procession when he heard 8-10 explosions and saw a fire.

"It seems the attackers had taken position inside the gathering," Dhaka police commissioner Asaduzzaman Mia told reporters, adding that the blasts were pre-planned and aimed at creating instability.

Police stepped up security at Shia mosques across the country immediately after the attack, while mourners in Dhaka's Mohammadpur neighbourhood said they had banned women and children from the procession.

"We've been observing this mourning procession here for centuries. But we've never seen any incident like this. We demand a quick and fair investigation into the blasts," a leader of the Shia community at Hussaini Dalan told reporters.

No one has yet claimed responsibility for the attack, police said.

The explosions come as tensions run high in Bangladesh after IS claimed its first attacks in the country.

Police and the authorities, however, have rejected the claim that IS was responsible, saying they do not believe the group is active in the country.

While the blasts are believed to be the first attack on Shias in Bangladesh, in the past two years banned militant groups have killed more than a dozen Sufi Muslims and attacked Hindus and Christians.

Experts say militants pose a growing danger in Muslim-majority Bangladesh, warning that a long-running political crisis has radicalised opponents of the government.

The killing of four atheist bloggers since the turn of the year has also undermined the government's efforts to play down the threat posed by hardliners, experts say.

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