Bangladesh's Supreme Court has rejected a final appeal by a top Islamist party leader convicted of war crimes in the country's independence war against Pakistan, confirming a death sentence given earlier by a special tribunal.

Chief Justice Surendra Kumar Sinha on Tuesday turned down the appeal by Mir Quashem Ali of the Jamaat-e-Islami party in the nation's capital, Dhaka.

The decision means there is now no legal bar to execute Ali. A special tribunal dealing with war crimes sentenced Ali to death in November 2014 for abduction, torture and killing.

Defense lawyers said Ali and his family would decide whether to seek clemency from the president.

Bangladesh says Pakistani soldiers, aided by local collaborators, killed 3 million people and raped 200,000 women in the 1971 war.