By Anis Ahmed

DHAKA (Reuters) - A Bangladesh war crimes tribunal sentenced a senior leader of the country's biggest Islamist party to life in prison on Tuesday, the second verdict in trials that have reopened wounds about the country's independence war and sparked riots.

Abdul Quader Mollah, 64, was found guilty of charges including murder, rape, torture and arson during Bangladesh's war to break away from Pakistan in 1971.

Activists of Mollah's Jamaat-e-Islami party skirmished with police in the capital, Dhaka, and other towns after the verdict. Police opened fire and used truncheons during demonstrations in the southeastern city of Chittagong and one person was killed, police and witnesses said.

The court delivered its first verdict last month, sentencing a former member of Jamaat-e-Islami and popular Islamic preacher to death, and a state prosecutor said he had been expecting the same sentence on Tuesday.

"We are not happy with the verdict and the merit of the judgment is not clear to us," said Mohammad Ali, a state prosecutor. "We wanted his death and are surprised by the lesser punishment handed out by the tribunal."

Quader Mollah made a "V" for victory sign while getting into a car after the verdict.

Jamaat's acting Secretary-General Rafiqul Islam Khan, denounced the verdict as dictated by authorities.

"It is a state-managed judgment," he said in a statement. "The tribunal pronounced the verdict as per the instruction of the government."

The party is demanding that the government dissolve the tribunal and release all of its leaders facing trial, including the party's former and current chiefs and their top lieutenants.

Bangladesh became part of Pakistan at the end of British rule in 1947 but it broke away 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 and numerous abuses were committed during the nine-month war.

The Jamaat-e-Islami has vowed to paralyze the country in protest against a tribunal that it says is politically biased.

Shops and businesses were shut and the streets were mostly empty in the capital and elsewhere as the Jamaat-e-Islami enforced a national strike against the verdict. The party called for the strike to extend into Wednesday.

Hundreds of war veterans massed outside the Dhaka court as the verdict was delivered, demanding that Mollah be put to death. There was tight security around the court premises, prompted by fears of a possible attack by Islamist militants.

Another 10 people, including two from main opposition Bangladesh Nationalist Party (BNP), are awaiting trial by the tribunal.

PROTESTS

Prime Minister Sheikh Hasina set up the tribunal in 2010 to investigate abuses during the 1971 conflict that claimed about 3 million lives and during which thousands of women were raped.

But critics say the prime minister is using the tribunal against members of the two biggest opposition parties, the BNP and the Jamaat-e-Islami.

Begum Khaleda Zia, Hasina's arch rival and leader of the BNP, has called the tribunal a "farce".

The ruling Awami party has rejected accusations that the tribunal is biased but it has been criticized by human rights groups for failing to adhere to standards of international law.

Awami leaders on Tuesday said they were also displeased over the verdict. "It did not reflect people's expectations," said State Minister for Law, Qamrul Islam.

Six people have been killed in recent weeks in violence related to the trials. About 150 people have been injured and a similar number arrested, police have said.

Jamaat has been accused of opposing the campaign for independence from Pakistan and helping the Pakistani army during the war in what was then East Pakistan. Jamaat denies that.

(Additional reporting by Ruma Paul; editing by Matthias Williams and Ron Popeski)