Dhaka: At least one person was killed and nearly 80 wounded Saturday in a bomb attack on the main Shiite shrine in the Old Dhaka of Bangladeshi capital as thousands gathered for the annual Ashura procession, police said.

Police said it was believed to be first time Bangladesh's tiny Shiite Muslim 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 Islamic State group.

Officers said a 14-year-old boy died on the spot after three small bombs were thrown at the complex of the Hossaini Dalan, the main Shiite site in the old Mughal quarter of Dhaka, at about 2:00 am Saturday (2000 GMT Friday).

"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.

The attacks come as Shiites around the world mark the holy month of Moharram, with Pakistan's Shiites also suffering sectarian violence this week after two suicide blasts killed at least 27 people.

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.

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.

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

Blast hit Ashura mourners

Ashura marks the climax of the holy month of Muharram when Shiites hold processions and gatherings to mourn the martyrdom of the Prophet Mohammed's grandson Imam Hussain at the Battle of Karbala in Iraq in 680 AD.

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 Hossaini Dalan, the most important prayer and congregation site for Bangladesh's Shiites.

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 reprters, adding that the blasts were pre-planned and aimed at creating instability.

Police stepped up security at Shiite 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 Shiite community at Hossaini Dalan told reporters. 

The explosions come as tensions run high in Bangladesh after the Islamic State group claimed its first attacks in the mainly moderate Sunni Muslim-majority country of 160 million people. 

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 Shiites in Bangladesh, in the past two years banned Islamist militant groups have killed more than a dozen Sufi Muslims and attacked Hindus and Christians.

Experts say Islamist 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.