Al-Qaeda's front group in Iraq has claimed a wave of bombings targeting Shiite areas of Baghdad that killed at least 21 people Sunday, in the latest violence to hit Iraq as it struggles with protests and a political crisis.

The al-Qaeda-affiliated Islamic State of Iraq (ISI) carried out the attacks "in revenge for alleged criminal acts by the Shiite-led government in Sunnis areas of the capital," said the SITE monitoring service, which tracks extremist Internet forums.

Three car bombs struck the sprawling Sadr City slum in the north of the city on Sunday, car bombs exploded in Ameen, Al-Husseiniyah and Kamaliyah in the east, and a roadside bomb blew up in Karrada in central Baghdad, security and medics there said.

Another roadside device went off in Saidiyah in the capital's south.

Al-Qaeda's front group is widely seen as weaker than during the peak of Iraq's sectarian bloodshed from 2006 to 2008, but is still capable of carrying out mass-casualty attacks on a regular basis.

Residents of Sadr City were enraged by the bombings, and hospitals in the area were quickly crowded with people searching for relatives.

"What did we do? We're always the victims of conflicts between politicians," one woman shouted.

The carnage could have been even worse.

The Baghdad Operations Command, which is responsible for security in the capital, said in a statement that security forces defused a total of six car bombs, including three in Sadr City.

Heavy security measures were put in place after the Sadr City attacks, with some areas closed off.

Gunmen also carried out two attacks in north Iraq on Sunday, killing a police captain in front of his home in Mosul and shooting dead a football player and wounding two others near Kirkuk, security and medical officials said.

The attacks brought the number of people killed in violence this month to at least 158, according to an AFP tally based on reports from security and medical officials nationwide.

The Baghdad bombings followed multiple attacks on Saturday that killed five people, including the head of Iraq's intelligence academy.

Two suicide bombers killed Brigadier General Aouni Ali and two of his guards, and more bombings resulted in the deaths of a judge and an army lieutenant.

Members of the security forces and judicial officials are also often targeted by militants in Iraq.

The latest violence comes as after nearly two months of anti-government protests centred on Sunni-majority areas in north and west Iraq, calling for the ouster of Iraqi Prime Minister Nuri al-Maliki, a Shiite, and amid a festering political crisis.

The demonstrations were initially sparked in December by the arrest of several guards of Finance Minister Rafa al-Essawi, a leading Sunni.

The longest-running protests have blocked a key trade route linking Baghdad to both Jordan and Syria.

As the demonstrations have since expanded markedly, the government has sought to curtail them by saying it has released thousands of detainees and raised the salaries of Sunni militiamen battling Al-Qaeda extremists.

It has also restricted movements in major cities on Fridays, when the largest protests are staged.

Maliki, meanwhile, has been tussling with a political crisis that has pitted him against many of his government partners barely two months before provincial elections, the country's first since March 2010 parliamentary polls.

A team of US Congressmen met with the Iranian dissident group MEK in Paris on Sunday and threatened to declare Iraq's prime minister a sponsor of terrorism after a deadly attack on an Iranian exile camp there.

The bi-partisan team, led by Dana Rohrabacher -- the chair of the sub-committee on Europe -- expressed strong support for the People's Mujahedeen of Iran (MEK) which has accused Iran's supreme leader Ayatollah Ali Khamenei of ordering a deadly attack on its camp in Iraq on February 9.

"If there is another attack on these helpless refugees obviously cleared by the government of Iraq, we will move in the US Congress ... and put forward a resolution declaring Prime Minister Maliki and his government state sponsors of terrorism," Rohrabacher said.