* Blasts hit Shi'ite districts across Baghdad
* Sunni insurgents trying to spark widespread violence
* Violence accompanying growing political unrest
Eight car bombs exploded in Shi'ite Muslim 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.
No-one claimed responsibility for the attacks, but Sunni Muslim insurgents have stepped up their activity since the beginning of the year in a bid to undermine the Shi'ite-led government and trigger deeper intercommunal fighting.
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.
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.
SUNNIS FEEL MARGINALISED
Violence in Iraq is increasing just as political tensions are rising against Shi'ite Prime Minister Nuri al-Maliki's power-sharing government made up of Shi'ite, Sunni and ethnic Kurds who split posts among them.
Thousands of Sunni Muslim 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 Shi'ite majority through the ballot box after the U.S.-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 Shi'ite 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 U.S. troops left.
More than 10 suicide attackers have struck security forces, Shi'ite targets and a Sunni lawmaker since the start of January.
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 Shi'ite funeral at the start of the month.
Iraqi Shi'ite leaders fear the war in neighbouring Syria - where Sunni rebels are fighting to oust President Bashar al-Assad, an ally of Shi'ite Iran - could further destabilise Iraq's delicate sectarian and ethnic balance.