Separately, two protesters were killed and 10 people wounded when a roadside bomb exploded in a central square, police and hospital officials said. They said the blast, which damaged several cars in the area, occurred in Tayaran square, about 500 metres from Tahrir square, the epicentre of anti-government protests in the capital.

Earlier, protesters repeatedly regrouped from under clouds of tear gas as they fought to tear down a concrete wall blocking access to Khilani Square. Security forces erected the barrier to keep the demonstrations from crossing a bridge that leads to the fortified Green Zone, the seat of government and many foreign embassies.

Tuk-tuk drivers ferried the injured back to makeshift medical tents stocked with saline used to douse demonstrators exposed to the tear gas. Many retched on the floor when they got there, saying the gas was the strongest they had ever experienced.

"We aren't afraid of them, the authorities," said Akeel, 21, who asked to be identified only by his first name.

Friday's deaths brought to four the number of protesters killed in the past 24 hours around the square, the centre of daily confrontations.

At least 320 people have been killed and thousands have been wounded since the unrest began on Oct. 1, when protesters took to the streets in the tens of thousands. They were outraged by what they said was widespread corruption, lack of job opportunities and poor basic services despite the country's oil wealth.

Hours before the clashes erupted, Grand Ayatollah Ali al-Sistani emphasised his support for the demonstrators in his weekly Friday sermon, saying none of their demands have been met so far and that electoral reform should be a priority. The senior cleric called for a new election law that would restore public confidence in the system and give voters the opportunity to bring "new faces" to power.

But Iraqi authorities appeared determined to disperse the protesters and keep them confined to a shrinking space in the capital's centre.

The confrontations in Khilani Square began on Friday afternoon after hundreds of protesters who breached the concrete barriers streamed into the square, where they were met by soldiers and riot police.

Early in the evening, live rounds were heard by The Associated Press several hundred metres from the square, and shortly after wafts of stinging tear gas caused a mass of protesters to run toward the medical tents.

Iraqi security and medical officials, who requested anonymity in line with regulations, said three protesters were killed and at least 25 others wounded.

The atmosphere at Tahrir was a striking contrast with the violence nearby. Baghdad's main square has been transformed into a carnival-like hub where protesters gather around music, comic art installations, pop-up food and street shops.

The demonstrations have kept up for weeks in central Baghdad and the mostly Shi'Ite southern provinces, despite the clamp down by Iraqi security forces.

Australian Associated Press