A suicide bomber on a bicycle blew himself up on a crowded street Thursday, killing six others and wounding dozens in the latest attack authorities blame on extremists who want to create an Islamic state in Bangladesh.

Among the wounded was another bomber police said failed to detonate his explosives.

Hundreds of people had gathered on a narrow street in the northern town of Netrokona after police safely detonated another bomb found in a building, when the suicide blast sent shrapnel ripping through the air.

There was no claim of responsibility, but officials blamed the attack on Jumatul Mujahideen Bangladesh, a banned Islamic group believed to be behind a wave of blasts that have killed 21 people in the past two weeks.

A police officer at the scene, Ali Hossain Faquir, said a handwritten leaflet warning police to follow Islamic law and stop protecting "man- made" laws was found near the site, about 80 miles north of the capital, Dhaka.

Prime Minister Khaleda Zia, who was visiting Saudi Arabia, expressed shock over the bombing.

"The masterminds behind the conspiracy have to be silenced with all our might," the United News of Bangladesh quoted Zia as saying.

A home ministry spokesman, Khondakar Monirul Alam, said Thursday's bombing was the work of those who committed the earlier attacks, but didn't name any groups.

The previous attacks largely targeted government offices and courts, and Alam told reporters in Dhaka the attackers have "adopted a new tactic, and targeted innocent people."

The suspected second bomber was under police guard in a hospital. Authorities did not say if the suspect had been questioned.

A police explosives expert said the bomb that was safely detonated — a metal container wrapped in red tape and packed with glass splinters — was "a small, not powerful bomb."

"It was probably used as a decoy to attract people," he said, speaking on condition of anonymity due to the continuing investigation.

The second bomb, however, was packed with high explosives and iron balls that tore through the crowd and instantly killed the bomber and three others. Three people died later from their wounds, police said.

At least 45 people, including nine police officers, were wounded, many seriously, witnesses and police said.

Rezaul Hossain Sumon, a 20-year-old college student with shrapnel wounds all over his body, said from his hospital bed in nearby Mymensing that about 400 people had been gathered in the street, hoping to catch a glimpse of the defused bomb.

He said he saw a man on a bicycle pull a cord tied to his body just before the explosion.

"I was close to the man and I saw him pulling the cord," Sumon said, groaning in pain. "I immediately collapsed."

A series of explosions this year have been blamed on militants who seek to establish Islamic rule in Bangladesh, a largely Muslim country governed by secular laws.

Zia has blamed the earlier bombings on Jumatul Mujahideen Bangladesh, calling the group's members "enemies of Islam."

Officials have said the banned group has up to 2,000 potential suicide bombers ready to strike.

The scope of the group's network was made clear on Aug. 17 when more than 400 small explosions were detonated across the country in near-simultaneous attacks that killed two people.

Witnesses to Thursday's blast described a scene of bloodied victims and screaming survivors.

"It was a terrible sight. People were screaming in pain all around," said Shymolendu Pal, a reporter for Dhaka's Ittefaq newspaper, who was in the crowd.

Shops and schools shut down shortly after the blasts as panic spread through Netrokona.