(Adds more attacks, quote from bomb witness, background)
BAGHDAD, May 16 (Reuters) - At least 17 people were killed by bombs in markets in Baghdad and attacks in northern Iraq on Thursday, police said, adding to a surge of sectarian-tinged violence in the past four weeks.
Attacks on Sunni and Shi'ite mosques, security forces and tribal leaders have mushroomed since security forces raided a Sunni protest camp near Kirkuk a month ago, igniting clashes and fuelling worries of a slide back into all-out sectarian war.
Iraq has grown more volatile as the civil war in neighbouring Syria strains fragile relations between Sunni and Shi'ite Muslims. Tensions are now at their highest since the last U.S. troops pulled out at the end of 2011.
Tthree car bombs exploded in busy markets in eastern and northeastern Shi'ite districts of the Iraqi capital, killing at least 14 people and wounding 26, police said.
"When the explosion happened, it was chaos. People were running everywhere to evacuate the victims. I saw two bakery labourers who were completely burned," said Hussein Mahdi, a shop owner at the scene of a blast in Sadr City.
In a separate incident, assailants with silenced weapons shot dead a prominent Sunni tribal leader in his car in southern Baghdad and seriously wounded his driver, police said.
In the northern city of Mosul, a suicide car bomber attacked a military checkpoint, killing two soldiers and wounding three, and a separate car bomb wounded two soldiers on patrol.
No group immediately claimed responsibility for the latest violence, which followed bombings that killed more than 35 people in Baghdad and the north on Wednesday.
According to the United Nations, April was Iraq's bloodiest month for almost five years, with 712 people killed.
The Iraqi government is embroiled in power struggles between majority Shi'ites, Sunnis and ethnic Kurds.
Minority Sunnis, who lost their dominance when the U.S.-led invasion toppled Saddam Hussein in 2003, have been protesting for months against Shi'ite Prime Minister Nuri al-Maliki.
Emboldened by the Sunni-led revolt in Syria, Iraqi Sunni insurgents, some linked to al Qaeda, have intensified attacks this year, threatening to drag Iraq back into communal strife. (Reporting by Kareem Raheem; Writing by Suadad al-Salhy; Editing by Patrick Markey and Alistair Lyon)