Abdul Quader Molla, 64, the fourth-highest ranked leader of the Jamaat-e-Islami party. (AFP Photo)
Supreme Court chamber judge Syed Mahmud Hossain stopped the execution of Abdul Quader Molla, a senior leader of the Jamaat-e-Islami party described by prosecutors as "the Butcher of Mirpur", until 10am Wednesday (0430 GMT), the court registrar said.
"The execution has been halted pending a hearing on Wednesday," the registrar told AFP, without elaborating.
Defence lawyer Shishir Munir said they were seeking a last-minute review of Molla's execution order as the country's constitution enshrines rights for a death-row convict to have his appeal heard in the Supreme Court.
Molla has been convicted of mass murder and rape during the Bangladesh's 1971 independence war against Pakistan.
Earlier in the day, Bangladesh's secular government had said it would go ahead with the execution of Molla at one minute past midnight -- despite a global outcry over the lack of a right to appeal.
In anticipation of the hanging, security has been tightened across the country and outside the jail in Old Dhaka where it was set to take place.
Observers worry Molla's execution could trigger massive protests in the unrest-plagued country, which is experiencing its worst political violence since independence.
At least 224 people have died in battles between opposition protesters, police and government supporters since January this year.
Bangladesh's deputy law minister Quamrul Islam had earlier announced the execution, adding the Jamaat leader had refused to seek a last-minute presidential clemency.
Prisons chief Main Uddin Khandaker said all preparations had been made for the execution.
Twenty-three members of Molla's extended family visited the jail to say good-bye to him, his son Hasan Jamil told AFP outside the prison gate earlier in the day.
"My father is being executed only because of his involvement in Islamic movement in the country," Jamil said, adding Molla looked calm hours ahead of when the execution had been scheduled, and had asked all family members to be "patient".
On Sunday, a tribunal signed an execution order for Molla, and sent it to the main jail in the capital Dhaka, raising speculation that the former journalist could be hanged any moment.
New York-based activist group Human Rights Watch and two UN Special Rapporteurs have warned that by executing Molla without giving him the opportunity to appeal for a review, the country could be breaking international law.
"What logic do they have to stop the execution?" Islam told AFP when asked about the criticism from rights experts.
"Did they stop the execution of Saddam Hussein?" he said, referring to the former Iraqi dictator who was hanged in December 2006.
Molla was convicted of rape, murder and mass murder, including the killing of over 350 unarmed Bengali civilians.
Prosecutors described him as the "Butcher of Mirpur", after a Dhaka suburb where he committed most of the atrocities.
A domestic war crimes court had originally sentenced him to life imprisonment in February -- but the sentence prompted protests by tens of thousands of secular demonstrators, who viewed it as too lenient.
Under pressure, the government amended the war crime law retroactively to allow it to appeal the sentence and seek the death penalty, which the Supreme Court then handed down in September.
UN expert Gabriela Knaul argued that any death sentence had to be "reviewed by a higher tribunal, as laid down in the International Covenant on Civil and Political Rights to which Bangladesh is a party".
Defence lawyers and Knaul had said the Supreme Court should have reviewed its own verdict, as enshrined in the country's constitution, which the government rejects.
Bangladeshi laws allow review of any death sentences in the Supreme Court, but prosecutors had said there is no such provision in the special war crime laws, which were enacted to prosecute suspected war criminals.
New York-based Human Rights Watch said the execution order was "particularly reprehensible" because the laws to hang Molla "were retroactively passed" in order to enable the death penalty, and where the right to appeal is not allowed.
Bangladesh regularly carries out the death sentence, 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 country's founding leader Sheikh Mujibur Rahman.