A series of bombings mainly targeting Shiite areas of Baghdad killed at least 21 people on Sunday, officials said, in the latest violence to hit Iraq as it struggles with protests and a political crisis.Three car bombs struck the sprawling Sadr City slum in the north of the city, 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 said.Another roadside device went off in Saidiyah in the capital's south.At least 21 people were killed and more than 120 were wounded in the attacks, the officials said.Residents of Sadr City were enraged by the bombings, and hospitals in the area were quickly crowded with people searching for relatives, an AFP journalist reported."What did we do? We're always the victims of conflicts between politicians," one woman shouted.Ali Kadhim, who owns a shop near the site of one blast, agreed, saying: "They always threaten each other, and it's us who die. The people are always the victims."And Hussein Mohammed, who was wounded and whose car was destroyed by one explosion, questioned how the bomb could have got past security forces into the area."I spent about two hours to enter Sadr City, so how could this car bomb enter?" he asked, his clothes smeared with blood and dirt. "Where is the security?"The carnage could have been even worse -- the AFP journalist saw soldiers apparently working to defuse another car bomb in the area.Heavy security measures were put in place after the Sadr City attacks, with some areas closed off.Security forces also searched cars at the main entrance to Sadr City and helicopters overflew the area, another AFP journalist said.Sunday's attacks bring the number of people killed in violence this month to at least 156, according to an AFP tally based on reports from security and medical officials nationwide.No group has yet claimed responsibility for the latest wave of attacks.But Sunni militants linked to the Al-Qaeda franchise in Iraq often target the Shiite majority in a bid to erode confidence in the central government and push the country back towards the bloody sectarian conflict of 2006-2007.The Baghdad bombings follow 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.