Bangladesh's highest court on Wednesday upheld the death sentence for the leader of the country's largest Islamist party for crimes during its 1971 independence struggle, paving the way for his execution within months.

The Supreme Court dismissed an appeal by Motiur Rahman Nizami, head of the Jamaat-e-Islami party, who was convicted of murder, rape and orchestrating the killing of top intellectuals when he was leader of a ruthless militia during the conflict.

"The court upheld the death sentence in three out of four charges. We're very happy," prosecutor Tureen Afroz told reporters.

"Most importantly, the death penalty was upheld for the killings of the intellectuals."

Nizami, 72, Jamaat's leader since 2000 and a minister in a former Islamist-allied government of 2001-2006, faces the gallows within months unless his case is reviewed by the same court or he is granted clemency by the president.

Three senior Jamaat officials and a key leader of the main opposition have been executed since December 2013 for war crimes, despite global criticism of their trials by a controversial war crimes tribunal.  

The court swiftly dismissed previous reviews of those four opposition leaders on death row, leading to their execution, the latest in November last year.

Hundreds of secular protesters who have been campaigning tirelessly for the trials of the Islamist leaders for their roles in the 1971 war burst into impromptu celebrations at a square in central Dhaka as the news of the court's decision came.

"This verdict brings an end to the long and painful wait for justice for the families of the victims of the war," Imran Sarker, head of a secular group, said, showing a V-sign to reporters.

Prosecutors said Nizami was the leader of a student wing of Jamaat during the war and turned it into the Al-Badr pro-Pakistani militia, which killed top professors, writers, doctors and journalists in the most gruesome chapter of the conflict.

Their bodies were found blindfolded with their hands tied and dumped in a marsh on the outskirts of the capital.

The killing was carried out based on a hit-list he ordered and the aim was to "intellectually cripple" the fledgling nation, they said.

Tight security  

Security was tight across the country after previous convictions of the Jamaat officials triggered the country's deadliest violence since independence with some 500 people killed, mainly in clashes between Islamists and police.

"We've stepped up security. It is sufficient to prevent any violence," deputy police commissioner Maruf Hossain Sorder told AFP ahead of the verdict.   

Nizami's lawyer Khandker Mahbub Hossain said he had hoped that his client would be acquitted.  

"We'll now decide the next course after consulting with him," he said.

Since it was established by Prime Minister Sheikh Hasina's government in 2010, the war crimes court, called the International Crimes Tribunal, has sentenced more than a dozen opposition leaders for war crimes.

Rights groups have criticised the trials, saying they fall short of international standards and lack any international oversight.

The secular government maintains the trials are needed to heal the wounds of the conflict, which it says left 3mn people dead.

Independent researchers put the toll much lower.