BAGHDAD (Reuters) - A series of car bombs exploded across the Iraqi capital late on Tuesday, killing at least 36 people in predominantly Shi'ite districts, police and medics said.

It was not immediately clear who had carried out the attacks, which appeared coordinated, but Sunni Islamist militants, including an al Qaeda-affiliate, have been regaining momentum in their insurgency against the Shi'ite-led government.

Tuesday's deadliest blast took place in Baghdad's northern Talbiya neighborhood, where a car bomb in a busy street killed nine people.

More than two years of civil war in neighboring Syria have aggravated deep-rooted sectarian divisions in Iraq, fraying an uneasy coalition of Shi'ite, Sunni and ethic Kurdish factions.

About 800 Iraqis were killed in August, according to the United Nations, with more than a third of the deadly attacks in Baghdad.

The bloodshed, 18 months after U.S. troops withdrew from Iraq, has stirred concerns about a relapse towards the sectarian slaughter of 2006-07.

(Reporting by Kareem Raheem; Writing by Isabel Coles; Editing by Robin Pomeroy)