Bangladesh's top court cleared the way Thursday for the execution of a senior Islamist leader charged with war crimes, just two days after he was given a dramatic last-minute reprieve from hanging.

Chief Justice Muzammel Hossain "dismissed" Abdul Quader Molla's appeal for a final review of his death sentence, removing his last legal option against execution, which could now be carried out as early as midnight Thursday.

Prison authorities said they were now "fully prepared" to execute Molla at one minute past midnight -- all Bangladeshi hangings are carried out at 1801 GMT -- but they would not confirm whether the execution would go ahead on Thursday.

The wife and children of Molla met the Jamaat-e-Islami leader at a jail in Dhaka for one last time.

"He has told us that he is proud to be a martyr for the cause of Islamic movement in the country," Molla's son Hasan Jamil told AFP, adding stepped-up security at the jail meant "they could hang my father tonight".

Security has also been tightened in the capital Dhaka with the authorities deploying paramilitary border guards in key flashpoints.

Islamists and opposition protesters rioted in several cities across the country, clashing with police with crude bombs and rocks, after the Supreme Court announced the brief verdict in the morning.

"There is now no legal bar to execute him," Attorney General Mahbubey Alam told AFP after the highest court decision.

Molla had been set on Tuesday night to become the first person put to death for massacres committed during Bangladesh's 1971 independence war, following a series of verdicts by a special war crimes court that have sparked deadly protests.

But a judge stayed the hanging just 90 minutes before his scheduled execution, amid international concern over the fairness of the war crime trials of mainly opposition leaders.

Molla, 65, was found to have been a leader of a pro-Pakistan militia which fought against the country's independence and killed some of Bangladesh's top professors, doctors, writers and journalists.

A key opposition official, he was convicted of rape, murder and mass murder, including the killing of more than 350 unarmed civilians.

Hundreds of secular protesters erupted in celebration hearing the latest verdict. They have been camping at Shahbagh square in Dhaka since Tuesday night, shouting slogans including: "Hang Quader Molla, hang war criminals".

Molla is one of five Islamists and other politicians sentenced to death by the International Crimes Tribunal, which the opposition says are politically motivated and aimed at eradicating its leaders.

The sentences have triggered riots and plunged the country into its worst violence since independence.

Some 231 people have been killed in street protests between secular and Islamist activists and with police, since January when the verdicts were first handed down.

Four opposition supporters were the latest killed on Thursday, all shot dead following clashes in the southern town of Laxmipur, police said.

Molla's lawyers had protested the original order, saying the death penalty was awarded based on evidence given by only one prosecution witness, who had also earlier given two different versions of the same event.

"He did not get justice," defence lawyer Khandaker Mahbub Hossain said.

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

New York-based Human Rights Watch and two UN Special Rapporteurs have warned that by executing Molla without the death sentence being reviewed, the country could be breaking international law.

UN Human Rights chief Navi Pillay wrote to Prime Minister Sheikh Hasina seeking a stay of the execution, saying the trial did not meet stringent international standards for the death penalty.

But deputy law minister Quamrul Islam rejected the criticism, saying "did they stop the execution of Saddam Hussein?"

"What logic do they have to stop the (Molla's) execution?" Islam told AFP.

Hasina's government says three million people died in the war, many at the hands of pro-Pakistan militias led by Jamaat leaders who opposed secession from the Islamic Republic of Pakistan on religious grounds.

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

Bangladesh regularly carries out the death sentence by hanging.

But Molla's death would be the most high-profile execution since January 2010, when five ex-army officers were put to death over the assassination of the nation's founding leader Sheikh Mujibur Rahman, Hasina's father.