Clashes between Iraqi protesters and security forces in central Baghdad killed at least two demonstrators overnight, security and medical sources said on Monday.
It was the first such deadly incident in months at Tahrir Square, which became a symbol of anti-government protests during months-long mass unrest last year.
The protesters had begun marching from Tahrir to nearby Tayaran Square chanting about worsening power cuts during a heat wave that has sent temperatures soaring above 50 degrees Celsius (122 degrees Fahrenheit).
Security forces tried to contain the march and fired tear gas, according to police, medics and protesters. The protesters threw stones and petrol bombs, a security source said.
Two protesters who were at the demonstration, and Ali Bayati, a member of Iraq’s semi-official High Commission for Human Rights, said security forces had fired live ammunition to disperse the crowd.
Prime Minister Mustafa al-Kadhimi said in a televised speech later on Monday that the protests "are a legitimate right and the security forces do not have the permission to fire even one bullet in the direction of the protesters".
He said he had opened an investigation and demanded results within 72 hours.
Military spokesman Yehia Rasool said in a statement that security forces had been given strict instructions not to use force against protesters unless necessary.
Medics at two hospitals in Baghdad said two men had been hit in the head and neck with tear gas canisters and died of their injuries. More than 26 protesters were wounded and several members of the security forces suffered minor injuries, police said.
Iraq's biggest anti-government protests in decades broke out last October and continued for several months, with hundreds of thousands of Iraqis demanding jobs, services and the removal of the ruling elite, which they said was corrupt. Nearly 500 people were killed.
The protests caused the resignation of Prime Minister Adel Abdul Mahdi, who was replaced in May by Kadhimi, a former intelligence chief.
Sporadic demonstrations have resumed in recent weeks in several Iraqi provinces, most recently over lack of electricity.
Clashes between security forces and protesters erupted again later on Monday in Baghdad and in other provinces.
A protester named Hussein described the death of one demonstrator in the overnight clashes.
"When Latif was martyred, he was holding only the flag. He didn't drop the flag until he was shot at by the police," he said. "He was just like any other young man at Tahrir Square, demanding rights for his family, for the people and for his children's future."
On Monday night, three rockets hit Iraq's Taji military base that houses U.S.-led coalition troops, but no casualties were reported, the military said in a statement.
There was no immediate claim of responsibility for the attack. Shortly later, two explosions hit Camp Speicher, a former U.S. base outside Tikrit, but caused no casualties, the military said, without giving further details.