At least 28 people have died and 65 injured in a spate of nine bombings mostly targeting Shia neighbourhoods of Baghdad, security and medical officials said.

Wednesday's blasts began at about 7:30am (04:30 GMT), the deadliest of which was in the central Sadria neighbourhood, where a parked car bomb went off at an outdoor market, killing five shoppers and wounding 15.

Other attacks took place in Shaab, Tobchi, Karrada, Azamiyah and Amil neighbourhoods. 

Al Jazeera's Imran Khan, reporting from Baghdad, said the death toll could have been higher as the attacks happened on on a public holiday declared by the government due to heavy rains.

Iraq is experiencing a surge in violence since April, following a deadly security raid on a Sunni protest camp in the country's north. Since then, more than 5,500 people have been killed, according to the United Nations.

No group immediately claimed responsibility for Wednesday's violence, but Sunni fighters linked to al-Qaeda's front group often set off co-ordinated bombings across Baghdad, typically targeting Shias.

The unrest has pushed violence to its highest level since 2008, when Iraq was recovering from the worst of its Sunni-Shia sectarian war.

Nouri al-Maliki, Iraq's Shia prime minister, has called for Washington's help to curb the bloodshed in the form of greater intelligence sharing and the timely delivery of new weapons.

But diplomats and analysts say the government is not doing enough to address the root causes of the unrest, particularly frustration in Iraq's Sunni minority which alleges it is mistreated by Shia-led authorities.

Officials fear the level of violence could rise further as fighters seek to destabilise the country ahead of landmark polls on April 30.

Source: Al Jazeera and agencies