DHAKA (AFP) - Attackers on Sunday hurled bombs and opened fire at a prison van in northern Bangladesh, killing a policeman and freeing convicts from a banned Islamic outfit involved in 2005 mass bombings.

Of the three convicts who escaped, two were members of the outlawed Jamayetul Mujahideen Bangladesh (JMB) and were awaiting execution while the third was serving a life sentence, police said.

The trio were convicted of involvement in a series of bombings across the country in 2005 that killed at least 28 people.

The police officer was shot dead after the attackers opened fire and hurled bombs at the prison van in Mymensingh district as the radicals were being taken to court for a hearing in another case, said local police officer Mahbub Hossain.

"The officer died on the way to hospital and two other officers were injured," Hossain told AFP.

The JMB set off hundreds of bombs nationwide between August and December 2005, including more than 400 small bombs in one day alone.

The then Islamist-allied government launched a crackdown on the banned group and prosecuted more than 1,000 of its members.

In 2007 an army-backed government hanged six JMB members, including its founder and leader Shaikh Abdur Rahman and his deputy. But the organisation is since believed to have regrouped.