* Nine car bombs explode in Baghdad
* Attack in northern town targets political party
* Violence increased since the start of 2013 (Adds details on attacks)
BAGHDAD, Aug 10 (Reuters) - A series of car bombs in mainly Shi'ite areas of Baghdad killed 50 people and wounded 140 on Saturday, police and medical sources said, part of a surge in violence in Iraq since the start of the year.
The nine separate explosions targeted markets and busy shopping streets, the sources said. The bombings, which appeared coordinated, were similar to attacks in Baghdad on Tuesday in which 50 were killed.
Attacks have multiplied in Iraq since the start of the year, with more than 1,000 people killed in July, the highest monthly death toll since 2008, according to the United Nations.
Sunni Islamist militants have been regaining momentum in their insurgency against the Shi'ite-led government and have been emboldened by the civil war in neighbouring Syria, which has stoked sectarian tensions across the Middle East.
Outside Baghdad, a suicide bomber detonated a bomb in a car on a busy street in the town of Tuz Khurmato, 170 km (105 miles) north of the capital, killing at least 10 people and wounding 45, medical and police sources said.
Tuz Khurmato is located in a particularly violent region over which both the central government and autonomous Iraqi Kurdistan claim jurisdiction.
Police believe the bomber was trying to reach the local headquarters of a Kurdish political party, but was unable to reach the building because of increased security in the area, a police source said. (Reporting by Kareem Raheem and Ahmed Rasheed in Baghdad, Mustafa Mahmoud in Kirkuk and Gassan Hassan in Tikrit; Writing by Sylvia Westall; Editing by Sonya Hepinstall)