BAGHDAD (Reuters) - Car bombs in busy Shi'ite Muslim areas of southern Iraq killed at least 18 people on Monday, medics and police sources said, taking the week's death toll to nearly 200 as sectarian violence intensifies.

Militant attacks have increased as the civil war in neighboring Syria puts further strains on fragile Sunni-Shi'ite relations, and tensions are at their highest since U.S. troops left Iraq more than a year ago.

Security forces' raid on a Sunni protest camp near Kirkuk last Tuesday triggered clashes that quickly spread to other Sunni areas in western and northern provinces.

The first of two blasts in Amara, 300 km (185 miles) southeast of Baghdad, ripped through a market where people were meeting to eat breakfast, and the second hit an area where laborers were gathering to look for daily work.

At least nine people were killed and 40 wounded in the Amara explosions, the sources said.

Another car bomb exploded in a market in Diywaniya, 150 km south of Baghdad, killing two people, police said.

"I was preparing to go to work when a big explosion shook my house and broke the glass in all the windows," said Woody Jasim. "I ran outside, the explosion was near my house and bodies were everywhere," he said.

A bomb in a parked car went off near a busy market in Kerbala, killing at least three people and a further four people were killed in an explosion near a Shi'ite worship site in Mahmudiya, about 30 km south of Baghdad.

No group immediately claimed responsibility for the attacks, but car and suicide bombings are trademarks of Sunni Islamist al Qaeda's Iraq wing, the Islamic State of Iraq.

Sunnis have been protesting since December against what they see as marginalization since the U.S.-led invasion overthrew dictator Saddam Hussein in 2003 and empowered majority Shi'ites.

The demonstrations had eased in the past month, but this week's army raid on a protest camp in Hawija, near Kirkuk, 170 km north of Baghdad, stoked Sunni anger and appears to have given insurgents more momentum.

(Reporting by Aref Mohammed in Basra, Kareem Raheem in Baghdad and Emad al-Khuzaie in Diywaniya; Writing by Suadad al-Salhy; Editing by Louise Ireland and Isabel Coles)