Anti-government demonstrators have spread out from their main protest camp on Tahrir (Liberation) Square onto three bridges linking the two banks of the river Tigris.

Security forces have erected concrete barriers on the bridges to hold protesters back, and late on Wednesday they fired tear gas and live ammunition at crowds gathering on the Al-Sinek and Al-Ahrar bridges.

One protester was shot dead by a live round and another died from a trauma wound sustained by a tear gas canister.

Rights groups have slammed security forces for firing the military-grade gas grenades directly at protesters instead of up in the air.

When shot at close range, the canisters can pierce demonstrators' skulls or chest, and advocacy groups have documented around two dozen such deaths.

The overnight confrontation also injured more than 50 people, including at least six who sustained gunshot wounds.

Authorities fear crowds could use the Al-Sinek bridge to reach the Iranian embassy in Baghdad and cross the adjacent Al-Ahrar bridge, further north, to protest at the Central Bank and other government buildings.

Protesters in Tahrir have slammed Tehran for propping up an Iraqi government they see as corrupt and inefficient, even accusing it of backing the use of violence against them.

More than 330 people have been killed since the protests broke out on October 1, according to an AFP toll, as authorities have stopped providing updated or precise figures.