The United Nations right chief on Wednesday expressed "serious alarm" at death sentences passed by a Bangladesh court on 152 soldiers over the massacre of scores of army officers in 2009.

High Commissioner for Human Rights Navi Pillay called the crimes committed in the mutiny "heinous" and "utterly reprehensible", but faulted the mass trial.

A total of 74 people were killed during the two-day mutiny in Dhaka, including 57 senior officers. Some were hacked to death or burnt alive before their bodies were dumped in sewers or shallow graves.

But Pillay added in a statement from Geneva that "justice will not be achieved" by conducting "trials that failed to meet the most fundamental standards of due process".

Bangladesh earlier on Wednesday defended the death sentences, insisting those convicted would have a chance to appeal and denying claims that confessions were extracted through torture.

"The convicts have at least two tiers of appeal," said Law Minister Shafique Ahmed, a day after a court in Dhaka delivered its verdicts against 823 soldiers on trial over the mutiny.

"No death sentence will be carried out unless they are confirmed in the higher courts," Ahmed added.

Pillay, however, called for an independent investigation into the allegations of human rights abuses, particularly custodial torture and killings after the mutiny.

"The results of the investigation should be made public and those responsible must be held accountable," she said.

She said the conviction and sentencing of each of the suspects "must be reviewed individually, and any evidence obtained under torture must not be admitted in court".

The UN opposes the death penalty under any circumstance, even for war crimes and genocide.

As well as the death sentences, the special court jailed more than 400 people on Tuesday at the end of the largest trial since independence in 1971.

Those sentenced to death had been accused of looting weapons and then embarking on a killing spree at a military base in February 2009, partly in anger that pleas for better pay and treatment had been ignored.

While confessions were read in court, rights groups said the army and an elite security force had tortured suspected mutineers.

Meenakshi Ganguly of the New York-based Human Rights Watch (HRW) said her organisation had documented the deaths of 47 soldiers taken into custody after the mutiny.

She said HRW activists had interviewed other suspects who suffered permanent disabilities or developed psychological problems after their interrogation by the army or the Rapid Action Battalion (RAB).

"Many of the accused did not know what they were charged with and didn't have legal representation," Ganguly told AFP.

"They said RAB and army officers who questioned them also tortured them in a bid to punish them even before they were found guilty."

Law Minister Ahmed rejected the allegations, asking: "Why would there be torture?"

Lead prosecutor Mosharraf Hossain also dismissed what he called "baseless" allegations, insisting that the trial was conducted in exemplary fashion.

"There were 654 witnesses, which is unprecedented in the world," said Hossain.

"The defendants' lawyers had plenty of time to question the witnesses. Every defendant had a lawyer."

The court on Tuesday also acquitted 271 people of involvement in the mutiny.

Lawyers for the soldiers on death row have said they will appeal. Executions by hanging are regularly carried out in Bangladesh.