More than 70 people were killed Monday in a series of bombings in Shi’ite neighborhoods of Baghdad, as sectarian violence continues to plague Iraq.

While no group has claimed responsibility for the attacks, Sunni Islamist insurgents and al Qaeda’s Iraqi branch have stepped up attacks in 2013, often targeting Shi’ite neighborhoods, Reuters reports.

More than a dozen blasts rocked markets and shopping areas across Baghdad on Monday, including a pair of blasts that killed at least 13 people in Sadr City, local police and hospital officials told Reuters. There were also several incidents in Anbar and Ninevah provinces, but officials did not provide further information, CNN reports.

"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," bystander Hassan Kadhim told Reuters. "People were shouting for help and blood covered their faces."

Relations between Shi’ite leadership and Sunni minority factions have deteriorated since December 2011, when United States troops exited Iraq. The ongoing conflict in Syria has has further destabilized Iraq’s delicate sectarian balance, Reuters reports.

More than 700 Iraqis were killed in attacks in April, according to a United Nations tally, the highest monthly total in nearly five years. And more than 300 people have died in May.

Iraq’s Sunni minority has staged street protests against Prime Minister Nouri al-Maliki since last December, accusing the Shi’ite leader of marginalizing their community after the 2003 fall of Saddam Hussein, Reuters reports. Violence spiked in April after the Iraqi army performed a raid on a Sunni protest camp in Hawija, causing armed clashes and a wave of new attacks.

The ongoing bombings of Sunni and Shi’ite mosques and monthlong surge in violence are heightening fears that Iraq will return to the levels of sectarian conflict that caused the deaths of thousands in 2006 and 2007, Reuters reports.