Central Jail, where Abdul Quader Mollah is being held in Dhaka, Bangladesh, is shown Tuesday.

Story highlights

NEW: U.N. human rights chief calls for a stay of execution

The execution of Abdul Quader Mollah has been put off until Wednesday

He is accused of war crimes dating back to 1971

The U.N. says the trial may not have been fair and an appeal process is needed

Dhaka, Bangladesh CNN  — 

Bangladesh postponed the hanging of an Islamist leader shortly before his execution was to take place Tuesday, his attorney told CNN.

Abdul Quader Mollah is now scheduled to be hanged Wednesday. His defense lawyers, meanwhile, are filing a petition for his sentence to be reviewed.

It was not immediately known why the government decided to postpone the execution.

The decision came a day after the United Nations called for the hanging to be halted.

On Tuesday, U.N. High Commissioner for Human Rights Navi Pillay joined the calls for a stay of execution.

Mollah was sentenced in September for alleged “crimes against humanity” dating back to 1971, during the country’s war for independence.

The ruling against him set off rioting in the streets and sparked a strike across the country.

Mollah was the assistant secretary general for the now-banned Jamaat-e-Islami party.

In February, he was convicted of war crimes by an international panel set up by the government to bring to justice those accused of atrocities.

He was originally sentenced to life in prison. Bangladesh’s supreme court then sentenced him to death. In the country’s legal system, that cannot be appealed.

Two U.N. human rights experts called on Bangladesh on Monday to halt the execution because of concerns that Mollah did not receive a fair trial.

“The right of appeal is of particular importance in death penalty cases,” said Gabriela Knaul, U.N. special rapporteur on the independence of judges and lawyers.

“Anyone convicted of a crime has the right to have his or her conviction and sentence reviewed by a higher tribunal, as laid down in the International Covenant on Civil and Political Rights to which Bangladesh is a party,” she said in a prepared statement. “This provision is violated where a court of final instance imposes a harsher sentence that cannot be reviewed.”

Christof Heyns, U.N. special rapporteur on summary executions, said capital punishment “may be imposed only following a trial that complied with fair trial and due process safeguards. … Only full respect for stringent due process guarantees distinguishes capital punishment as possibly permitted under international law from a summary execution, which by definition violates human rights standards.”

In a statement Tuesday, Pillay called for a stay, saying the trial had not met stringent international standards for the death penalty, the U.N. said in a statement.

The United Nations opposes the death penalty in any circumstance.

152 soldiers sentenced to die for mutiny in Bangladesh

CNN’s Brian Walker and Josh Levs contributed to this report.