BAGHDAD (Reuters) - Car bombs in two towns south of Baghdad and in the Iraqi city of Najaf killed a total of 20 people on Sunday and wounded 80, police and hospital sources said, in one of the most violent days of the past two weeks.

Three car bombs killed 11 people and wounded 38 in Mahmudiya, a town 30 km (20 miles) south of Baghdad, according to police.

The first detonated in a car in a parking lot, the second in another car as police arrived at the scene and a third at the town's police station, the police sources said.

In Madaen, a town 30 km (20 miles) southeast of the Iraqi capital, two bombs killed five people and wounded 14 in a crowded market, police and hospital sources said.

And car bombs planted in a busy trading street in Najaf, 160 km (100 miles) south of Baghdad, killed four people and wounded 28, Interior Ministry sources said.

Although violence in Iraq has eased since a peak in 2006-2007 when tens of thousands were killed, insurgents still carry out deadly attacks, especially around the capital.

The past two weeks have seen a lull in violence in the lead-up to the Muslim holy month of Ramadan, which started in Iraq on Saturday.

Last month at least 237 people were killed and 603 wounded in attacks, making it one of the bloodiest months since U.S. troops withdrew at the end of last year.

(Reporting by Kareem Raheem; Writing by Sylvia Westall; Editing by Kevin Liffey)