DHAKA: At least 50 people including policemen were injured in Bangladesh on Monday as Islamist activists protested against the prosecution of their leaders on charges stemming from a war of independence 40 years ago, police and witnesses said.

Protesters set off crude explosives and threw bricks at police who tried to disperse them with teargas, batons and some shots in the air, witnesses said.

"The Islamists vandalised dozens of vehicles and set fire to two buses in Motijheel commercial area and other places in the city," a police officer said.

Islamist party spokesman were not available for comment.

Police detained about 20 activists, reporters on the scene said, and the disturbances disrupted traffic on city-centre roads. Similar protests broke out in the northern town of Rajshahi and in Chittagong in the southeast.

Bangladesh became part of Pakistan at the end of British rule in 1947 but it broke away from Pakistan in 1971 after a war between Bangladeshi nationalists, who were backed by India, and Pakistani forces.

Some factions in Bangladesh opposed the break with Pakistan.

A Bangladeshi war crimes tribunal began work in mid-2011 to investigate some of the violence during the nine-month war when up to three million people were killed and thousands of women were raped.

Last week, the tribunal reached its first verdict, sentencing a former member of the Jamaat-e-Islami party and a popular Islamic preacher, Abul Kalam Azad, to death in absentia.

Azad has been missing since April last year but the government says it is trying to find him.

Azad was charged with collaborating with Pakistani forces in the murder of Hindus, a minority in the majority-Muslim state. In one case, he was accused of killing at least 12 Hindus while shooting indiscriminately along with Pakistani soldiers.

Jamaat has been accused of helping the Pakistani army in acts of violence, which it denies.

Another 11 people, nine of them Jamaat leaders, are facing trial.

Over the last few months Jamaat activists and members of its student wing have launched violent protests in Dhaka and other cities, demanding an end to the trials.

Human Rights Watch has said the law under which the accused were being tried fell short of international standards of due process. It cited defence lawyers, witnesses and investigators as saying they had been threatened during the trial.

The ruling party of Prime Minister Sheikh Hasina, who set up the tribunal, has denied the accusations of bias.