Two bombs exploded near Sunni mosques in the Iraqi capital as worshippers left after Friday prayers, killing six people, while seven more died in attacks targeting security forces, officials said.
The bombs -- one near a mosque in the Dura area of Baghdad and the second in Jihad -- also wounded at least 22 people.
The blasts were the latest in a series of sectarian attacks in the city, and came a week after two bombs in a Sunni mosque north of the capital killed 18 people.
Last Saturday, bombings targeting Shiite mourners in Baghdad killed 73 people, while an attack on a Sunni funeral killed 12 the next day.
And another bombing against Sunni mourners in Baghdad killed 15 on Monday.
There are persistent fears of a return to the all-out Sunni-Shiite violence that peaked in 2006-2007 and killed tens of thousands of people.
The UN refugee agency said this week it was "increasingly concerned about the situation in Iraq, where recent waves of sectarian violence threaten to spark new internal displacement of Iraqis fleeing bombings and other attacks".
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Some 5,000 Iraqis have been displaced this year, joining more than 1.13 million who had previously fled or been forced from their homes, it said.
Other attacks on Friday targeted security forces in north Iraq.
In Nineveh province, a bomb killed a police colonel and two of his guards, and wounded four others.
A suicide bomber also detonated an explosives-rigged vehicle near an army base in the province, killing two soldiers and wounding 10 other people, while a bomb near a policeman's house killed his mother.
And gunmen shot dead a police colonel in Kirkuk province.
Militants including those linked to Al-Qaeda frequently carry out attacks against Iraqi security forces.
The latest violence brings the death toll to more than 730 people in September and more than 4,550 this year, according to AFP figures based on security and medical sources.