BAGHDAD >> Anti-government protesters in Iraq seized control of a third strategic Baghdad bridge today, while others blocked roads with burning tires in parts of central and southern Iraq, halting traffic and paralyzing work following a call for a national strike.

Protesters retook control of half of Ahrar Bridge, which leads to the other side of the Tigris River near the heavily fortified Green Zone, the seat of Iraq’s government. Security forces deployed on the other side of the bridge and erected concrete barriers to keep protesters from pushing into the area.

At least 320 people have been killed and thousands wounded since the unrest in the capital and the mostly Shiite southern provinces began on Oct. 1. Protesters have taken to the streets in the tens of thousands over what they say is widespread corruption, lack of job opportunities and poor basic services despite the country’s oil wealth.

Bridges leading toward the Green Zone have been a frequent flashpoint in the protests. Demonstrators had taken control of these bridges earlier this month but were later repelled when security forces took harsh suppressive measures.

Ahrar Bridge was the third retaken by the protesters, after seizing part of Sinak Bridge and central Khilani Square the previous day following fierce clashes. They were also present in Jumhouriyya Bridge adjacent to Tahrir Square, the epicenter of the protest movement.

Iraqi security forces withdrew from Khilani Square after firing live ammunition and tear gas against protesters trying to tear down a concrete barrier blocking entry to the square.

Protesters also took control of a five-story parking garage adjacent to the bridge, giving them a bird’s eye view over the Green Zone and the street below, mirroring tactics employed in Tahrir Square, where they occupied an iconic 14-story Saddam Hussein-era building that has become a reference point for demonstrators.

Two people were wounded when security forces fired tear gas canisters in renewed confrontations on Baghdad’s famous Rasheed Street, its oldest avenue and cultural center known for its crumbling houses.

In the southern port city of Basra and in cities like Nasiriyah, Amara and Kut, protesters set tires ablaze to close off roads, keeping employees from reaching their work places. Schools, universities and other institutions closed for the day.

In parts of Baghdad, particularly the sprawling Sadr City neighborhood, protesters sat in the middle of the streets to prevent employees from getting to their workplaces. They also blocked roads with motorcycles and tuk-tuks, snarling traffic.

“There will be no offices open until the last corrupt person is removed,” one protester said, declining to be identified for security reasons. “Only then we will pull out from here.”

The roadblocks are partly in response to a call by influential Shiite cleric Muqtada al-Sadr for a voluntary strike to keep up the pressure on politicians.

The leaderless, mass protests aim to sweep aside Iraq’s political elite, blamed for massive corruption.