Reuters reports: More than 70 people were killed in a wave of bombings in markets in Shi’ite neighborhoods across Baghdad on Monday in worsening sectarian violence in Iraq.

No group claimed responsibility for the blasts. But Sunni Muslim Islamist insurgents and al-Qaeda’ s Iraqi wing have increased attacks since the beginning of the year and often target Shi’ite districts.

More than a dozen blasts tore into markets and shopping areas in districts across the Iraqi capital, including twin bombs just several hundred meters apart that killed at least 13 people in the capital’s Sadr City area, police and hospital officials said.

“A driver hit another car and left pretending to bring traffic police. Another car rushed to take him away and right after his car exploded among people who had gathered to see what was happening,” said bystander Hassan Kadhim. “People were shouting for help and blood covered their faces.”

Tensions between the Shi’ite leadership and the Sunni Muslim minority are at their worst since U.S. troops left in December 2011, and the conflict in Syria is straining Iraq’s fragile communal balance.