More than 340 people have died and thousands have been wounded since rallies against widespread graft and unemployment erupted in Baghdad and the mostly-Shiite south last month.

Protesters have occupied the capital's iconic Tahrir (Liberation) Square for four consecutive weeks, spreading out onto bridges leading to the western bank of the river Tigris.

The last deaths came as riot police fired tear gas and live rounds to keep crowds from crossing over, a medical source told AFP.

Two of them were shot dead and the third died from trauma injuries from a tear gas canister. Another 30 protesters were wounded.

The bridges lead to the Green Zone housing parliament, the prime minister's office, a number of ministries and the central bank -- as well as foreign embassies.

Security forces have set up concrete barriers and checkpoints to protect the zone from angry protesters they fear may try to storm buildings.

Four protesters were killed and dozens wounded in the same area on Thursday.

Demonstrators have relied heavily on sit-ins at schools, government offices and other public infrastructure in Baghdad and the south.

On Friday, rallies gripped the largely agricultural southern towns of Hillah, Nasiriyah and Diwaniyah, as well as the two Shiite holy cities of Najaf and Karbala.

In protest-hit Kut, a local tribal leader said protesters would keep up the pressure on authorities.

"We are determined to keep demonstrating until our demands are met: the government's resignation and parliament's dissolution," said Nasir al-Qassab.

"We reject proposals from the government... They're just trying to procrastinate," Qassab said, referring to proposed social reforms and constitutional amendments.