Adam Schreck

BAGHDAD: Officials in Iraq are growing increasingly concerned over an unabated spike in violence that claimed at least another 33 lives on Thursday and is reviving fears of a return to widespread sectarian fighting.

Authorities announced plans to impose a sweeping ban on many cars across the Iraqi capital starting early today in an apparent effort to thwart car bombings, as the United Nations envoy to Iraq warned that “systemic violence is ready to explode.”

Prime Minister Nouri al-Maliki, meanwhile, was shown on state television visiting security checkpoints around Baghdad the previous night as part of a three-hour inspection tour, underscoring the government’s efforts to show it is acting to curtail the bloodshed.

Iraqi security forces are struggling to contain the country’s most relentless round of violence since the 2011 U.S. military withdrawal.

The rise in violence follows months of protests against the Shiite-led government by Iraq’s Sunni minority, many of whom feel they’ve been marginalized and unfairly treated since the 2003 U.S.-led invasion. Tensions escalated sharply last month after a deadly crackdown by security forces on a Sunni protest camp.

Sunni militants, including al-Qaida, have long targeted Iraq’s Shiite majority and government security forces. But Sunni mosques and other targets have also been struck over the past several weeks, raising the possibility that Shiite militias are also growing more active.

Several members of the security forces were killed in Thursday’s bombings. The attacks also included an assassination attempt by a suicide bomber targeting a provincial governor in the country’s Sunni-dominated west.

“These daily patterns of car bomb attacks ... in Baghdad and some other cities [are] really unacceptable for the people of Iraq, who have suffered so much,” Foreign Minister Hoshyar Zebari said Thursday.

“It’s the government’s responsibility to redouble its efforts, to revise its security plans, to contain this wave, to prevent it from sliding into sectarian conflict and war,” he added. “That should not happen again.”

The spike in violence, which has gained momentum since the middle of the month, is raising worries that Iraq is heading back toward the widespread sectarian bloodletting that spiked in 2006 and 2007 and pushed the country to the brink of civil war.

More than 500 people have been killed in May. The month before was Iraq’s deadliest since June 2008, according to a United Nations tally that put April’s death toll at more than 700.

“Iraq is a reactor that’s overheating and there’s little coolant available,” said Ramzy Mardini, an analyst at the Beirut-based Iraq Institute for Strategic Studies. “Iraq’s nascent politics is not equipped to sustain the current dangerous levels of internal and external pressure. There needs to be an off-ramp to relieve some of the pressure.”

The vehicle ban coming into effect today applies to cars bearing temporary black license plates. Those plates are common in post-war Iraq, where for years it was difficult to obtain new ones. They are typically on older-model vehicles and are more difficult to trace, and authorities say they are frequently used in car bombings.

Most of Thursday’s blasts erupted in Baghdad.

Car bombs killed four in the northeastern Shiite neighborhood of Binouq, and three died in a bombing at a market selling spare car parts in central Baghdad, police said.