"According to eyewitnesses and forensic data, hunting rifles killed" two protesters, Interior Minister Othman al-Ghanemi told reporters on Thursday.

The minister gave the names of three policemen and displayed the arms and ammunition they had purportedly used.

Hunting rifles were in the personal possession of the three, "who decided on their own account to make use of them", he told reporters.

They have confessed to using the weapons and have been suspended from their duties, Ghanemi said, adding that judicial proceedings were underway.

The account of the killings, which took place earlier this week, differed from that given previously by medics.

Medical sources said three protesters died but authorities mentioned only two deaths on Thursday.

Medics also said the three dead protesters had been hit by tear gas canisters, rather than live rounds, a version of events the government has denied.

Ghanemi said an investigation had been opened because the federal police had deployed "to fire live rounds in the air", contravening orders not to use live fire by the prime minister, who heads the armed forces.

Mustafa al-Kadhemi came to power in early May, replacing Adel Abdel Mahdi, whose position became untenable amid months of protests stretching back to October last year.

The new premier has been keen to distance himself from his predecessor, who accused an unnamed third force of being behind the deaths of security personnel and hundreds of protesters.

The government announced on Thursday that 560 people had been killed in protests since October, a tally it said included those slain early this week.

Nearly all the dead were demonstrators killed at the hands of security forces, said Hosham Dawod, an adviser to the premier handling an investigation into the protests.

The families of each of the 560 victims will each be compensated with 10 million Iraqi dinars (around $8,400), Dawod said.