At least five protesters and two policemen have been killed in the Iraqi capital during a rally by thousands calling for an overhaul of the electoral system, according to police.

Iraqi security forces fired tear gas and rubber-coated bullets at thousands of supporters of Muqtada al-Sadr, an influential Shia leader, who were demonstrating on Saturday near Baghdad's Green Zone to press for electoral changes.

At least 320 protesters and seven police officers were wounded as violence gripped the rally.

The Associated Press news agency, quoting hospital officials, said the officer died of a bullet wound.

"There were seven dead as a result of the violence. Two of them are from the security forces and the other five are protesters," a police colonel told AFP news agency on condition of anonymity.

He put the number of people hurt in the chaos at more than 200.

Sadr's demands

Sadr has accused the elections commission of being corrupt and called for the commission's members to be changed, according to a statement from his office.

Rising to his call to protest, demonstrators gathered near the Green Zone - a cluster of embassies and government buildings - to demand an overhaul of the commission that supervises elections before a provincial vote due in September.

Riot police fired tear gas when the crowd tried to move towards the zone, which also houses international organisations and the homes of prominent politicians.

Shots rang out in central Baghdad, as security forces used live fire and tear gas to disperse the crowds.

"We will not give in to threats," said Serbat Mustafa, the head of the electoral commission, in an interview with a local Iraqi television channel on Saturday afternoon.

Mustafa said he would not offer his resignation and accused Sadr of using the commission as a political "scapegoat".

Haider al-Abadi, Iraq's prime minister, called on the demonstrators to remain peaceful and to "abide by the law".

The Najaf-based Sadr, however, gave a green light to an escalation of the protests, telling his supporters: "If you want to approach the gates of the Green Zone to affirm your demands and make them heard to those on the other side of the fence ... you can."

Sadr has been a fierce critic of Abadi, and, last year, protests that included many of his followers breached the Green Zone twice.

Eventually, he called for restraint on Saturday but warned Abadi not to turn a deaf ear.

"I urge him to deliver those reforms immediately, listen to the voice of the people and remove the corrupt," he said in a statement.

Rockets hit Green Zone

Late on Saturday, the body coordinating security operations in Iraq said several Katyusha-type rockets were fired at the Green Zone from within Baghdad.

"Several Katyusha rockets fired from the Baladiyat and Palestine Street areas landed in the Green Zone," the Joint Operations Command said in a statement, without specifying who fired them.

Police and interior ministry officials confirmed to AFP that several rockets were fired at the area, but could not specify what the presumed target was nor whether there were any victims.

"Several rockets, maybe six or seven, struck the Green Zone. I can hear the siren is being sounded in the area," Maysoon Damaluji, a legislator who lives in the protected area, told AFP.

A diplomat who also lives in the Green Zone said he heard four blasts.