Authorities called Ali's family to the prison and intensified security around the Kashimpur Central Jail on the outskirts of the capital.
"Twenty-two members of his family reached the jail to see him (Ali) for the last time," private TV channels reported quoting an official of the jail where Ali is kept in an isolated cell.
He, however, evaded a direct question if Ali was set to be executed by tonight, saying: "We are always ready."
Five war crimes convicts were executed so far since Bangladesh initiated a trial process in 2010 for the 1971 war criminals. They were hanged soon after their family members saw them off for the last time.
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Yesterday, Ali declined to seek presidential mercy as the last resort to save his neck after the Supreme Court rejected his final review petition earlier this week.
"Now there remains no bar in executing him anytime... The government can make preparation for his execution," attorney general Mahbubey Alam said yesterday.
Alam earlier said that unlike the ordinary cases, the condemned war criminals were not entitled to a certain period before being hanged after the apex court verdict as they were tried under a special law.
Ali was conveyed the verdict on Wednesday, a day after the Supreme Court upheld an earlier ruling that had handed down a death sentence, following which he had sought time to decide over seeking the clemency.
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Authorities have deployed paramilitary Border Guard Bangladesh (BGB) troops to patrol Dhaka streets and secure the jail complex.
Elite anti-crime Rapid Action Battalion (RAB) and armed policemen have installed makeshift street checkposts in several areas of the city to prevent any possible sabotage coinciding with the execution.
"Law enforcement agencies have been kept on high alert," a Home Ministry spokesman said.