An Iraqi court on Wednesday sentenced 24 men to hang over the June 2014 massacre by jihadists and allied militants of hundreds of mostly Shiite military recruits in Tikrit.

The central criminal court in Baghdad handed 24 of 28 defendants the maximum sentence over the "Speicher" massacre, named after the base from which the victims were captured before being executed.

"After deliberations, the court finds that the evidence collected is sufficient to convict 24 defendants," said the judge. "The court decided they will be executed by hanging."

All 24 denied any involvement in the massacre, committed during the first days of the Islamic State group's broad offensive in Iraq.

The other four defendants were acquitted.

Around 600 bodies of victims have been exhumed from burial sites in the Tikrit area. Footage released by IS last year shows some of the captured recruits were shot and pushed into the Tigris river.

The defendants were brought into the courtroom blindfolded, handcuffed and chained by their feet.

Proceedings were conducted expeditiously and rights groups criticised a trial they said was far from meeting international standards and did not do justice to the scale of the crime.

Relatives of some of the Speicher massacre victims were heard by the court asking that the perpetrators of what is one of IS's worst atrocities be punished.

A court-appointed defence lawyer spoke briefly to ask for leniency but did not challenge the evidence, which consisted mainly of confessions the defendants themselves claimed were obtained under torture.

- 'Unfair trial' -

The judge showed one defendant a grainy printout of a grab from the video footage of the massacre.

"Is that you?" he asked. The accused answered negatively, as did several fellow defendants when the judge flashed confession documents and asked them to confirm their authenticity.

Some defendants swore they were not even close to Tikrit on June 11 last year, others that they never saw a lawyer.

"We are still looking at the full details of the case, but the Speicher trial bears the hallmark of unfair trials that have seen thousands of those accused of terrorism in Iraq sentenced to long prison terms or to death," Amnesty International said in a statement to AFP.

"Often confessions extracted under torture and denied by the defendants in court were used to secure convictions. Today's trial seems to continue that pattern despite statements these men will get a fair trial," it said.

The highest estimate for the number of men murdered in the Speicher massacre is 1,700. Tikrit was retaken from IS in April and the exact circumstances of the massacre have yet to be established.

"The speed of the trial is highly dubious," said Cristoph Wilcke, Iraq researcher at Human Rights Watch.

"This is different from an ordinary crime, proceedings have to be even more detailed, transparent and fair. It is clear that this trial did not meet those standards," he told AFP.

According to Amnesty, Iraq executed at least 61 people in 2014, ranking fourth among countries carrying out the most executions after China, Iran and Saudi Arabia.

Combined with a call by the country's top Shiite cleric Grand Ayatollah Ali al-Sistani for Iraqis to take up arms against them, the Speicher massacre played a key role in the mass recruitment of Shiite volunteers to fight the jihadists.

One of the spots where the Speicher cadets were executed is a police building in the sprawling Tikrit palace complex former president Saddam Hussein built in his hometown.

The quay where the victims were shot in the head and pushed into the Tigris has, since Tikrit was retaken, been turned into an improvised shrine.

Relatives, many of whom may never have a body to bury, have streamed to the site over the past two months along with fighters, delegations of officials, students and others.