BAGHDAD (Reuters/AFP) - Eight car bombs exploded in Shia neighbourhoods across Iraq's capital Baghdad on Sunday morning, killing at least 28 people in blasts that tore into shops, restaurants and busy commercial streets.

One blast tore off shop fronts in Qaiyara district while another left the remains of a car and its twisted engine littered across a high street in the busy, commercial Karrada district packed with restaurants and shops. "I was buying an air conditioner and suddenly there was an explosion. I threw myself on the ground. Minutes later I saw many people around, some of them dead, others wounded," said salesman Jumaa Kareem, his jacket spattered with blood in Habibiya district, which was also hit.

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, security and medics said. Another roadside device went off in Saidiyah in the capital's south.

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.

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. Security forces also searched cars at the main entrance to Sadr City and helicopters overflew the area, another AFP journalist said.

Also on Sunday, gunmen killed a police captain in front of his home in Mosul in north Iraq, security and medical officials said.

Sunday's attacks bring the number of people killed in violence this month to at least 157, 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.

Sunday's blasts followed the assassination of a senior Iraqi army intelligence officer on Saturday, the latest in a wave of suicide bombings since January that indicate insurgent determination to stoke sectarian tensions.

Violence in Iraq is increasing just as political tensions are rising against Prime Minister Nuri al-Maliki's power-sharing government made up of Shia, Sunni and ethnic Kurds who split posts among them.

Thousands of Sunni protesters have rallied daily since late December in western provinces against what they see as the marginalisation of their minority sect, and calling for Maliki to step down.

Many Iraq Sunnis feel they have been sidelined and unfairly targeted by security forces since the fall of Saddam Hussein and the rise of the country's Shia majority through the ballot box after the US-led invasion.

The country's fragile power-sharing government has been paralysed by political infighting since the last American troops, who invaded the OPEC country to oust Saddam in 2003, withdrew more than a year ago.

Maliki has offered concessions to Sunni protesters, but the Shia premier has warned against allowing insurgents and hardline Islamists to hijack the demonstrations.

Violence in Iraq is still far from the sectarian bloodletting that killed tens of thousands in 2006-2007, though insurgents have carried out at least one big attack a month since the last US troops left.

In the most recent attacks, a suicide bomber killed the head of the army's intelligence school on Saturday after storming his home in a northern town. Another suicide bomber killed 26 at a funeral at the start of the month.