DHAKA (AFP) - Six people were killed in Bangladesh including three protesters who were shot dead by police on Saturday as Islamists vented their fury at the execution of one of their leaders for war crimes.

The deadly clashes erupted two days after the government hanged senior leader of the Jamaat-e-Islami party, Abdul Quader Molla, for war crimes - the first person to be executed for his role in the country's bloody 1971 war of independence from Pakistan.

Police said they opened fire during clashes with thousands of rampaging Jamaat protesters in the southern town of Companyganj, leaving three people dead and dozens injured.

"We fired rifles in self defence after at least 8,000 Jamaat supporters attacked us with guns and torched four government offices with gunpowder," local police chief Shafiqul Islam told AFP.

He added that the bullet-ridden bodies of three Jamaat activists had been recovered.

Three other people, a Jamaat supporter and two ruling party activists, were killed in the northern town of Ramganj after hundreds of protesters of Jamaat and its main ally the Bangladesh Nationalist Party (BNP) attacked a convoy of ruling party member of parliament, local police chief Babul Akter told AFP.

The deaths raised the tally in clashes since the execution of Jamaat leader to 12. Hundreds were also injured, many hit by bullets.

Molla had been found guilty in February by a much-criticised domestic tribunal of having been a leader of a pro-Pakistan militia that fought against the country's independence and killed some of Bangladesh's top professors, doctors, writers and journalists.

He was convicted of rape, murder and mass murder, including the killing of more than 350 unarmed civilians. Prosecutors called him the "Butcher of Mirpur", a Dhaka suburb where he committed most of the atrocities.

Fears that the execution could spark further unrest, in a country where political violence is intensifying in the build-up to deeply divisive elections, were soon realised as the Islamists rioted in street battles in towns and cities.

Rampaging Jamaat activists firebombed train stations, set fire to businesses and houses belonging to ruling party supporters and blockaded key highways, they said.

Jamaat has called the execution a "political murder" and warned of exacting revenge for "every drop" of Molla's blood.

Molla was one of five Islamists and other politicians sentenced to death by the domestic court known as the International Crimes Tribunal, which the opposition says is aimed at eradicating its leaders.

The sentences have triggered riots and plunged the country into its worst violence since independence. Some 242 people have now been killed in street protests since January, when the verdicts were first handed down.

The government says three million people died in the 1971 war, many at the hands of militias led by Jamaat leaders who opposed the then East Pakistan seceding from Islamabad.

Independent researchers put the death toll at between 300,000 and 500,000 people.