Delwar Hossain Sayeedi

Bangladeshi police officers escort Delwar Hossain Sayeedi, centre. A special war crimes tribunal in Bangladesh sentenced Sayedee to death for crimes stemming from the nation's 1971 fight for independence. Photo: AP

DHAKA: Clashes between police and supporters of Bangladesh's biggest Islamic party killed 35 people after a war crimes tribunal sentenced one of the group's leaders to death for atrocities committed four decades ago.

Police tightened security amid concern there would be further violence after Friday prayers.

The dead included three policemen, while 800 people were injured when Jamaat-e-Islami activists rioted after the verdict was announced against Delwar Hossain Sayedee, 73, the Samakal newspaper said.

A policeman uses a baton on an activist of Jamaat-e-Islami, Bangladesh's biggest Islamist party, during a clash at Jatrabari in Dhaka.

The death sentence verdict was considered a a politically charged decision that sparked violent protests. Photo: Reuters

The clashes expose the deep divisions in Bangladesh over the war that led to its independence from Pakistan in 1971.

While mainly secularist protesters have been occupying a square in Bangladesh's capital since February 5, demanding harsher penalties for those found guilty by the tribunal, supporters of Islamic parties say the trials are politically motivated.

The Islamic Foundation, which is run by the Ministry of Religious Affairs, asked mosques to avoid inflaming the situation.

The group made the appeal after protesters at a mosque on February 22 threw stones at police and set fire to prayer mats in protest against the war crimes trial and Facebook postings they said were blasphemous.

Sayedee, who was in court when the verdict was delivered, faced 19 charges including the murder of civilians, collaborating with the Pakistani army, torching homes and carrying out atrocities against Hindus, according to a court document.

Eight charges were proved beyond reasonable doubt, prosecutors said.

''It's a victory day, it's a day of joy. Through this verdict, the nation is seeing the resurgence of liberation war spirits,'' the Attorney-General, Mahbubey Alam, said on Thursday.