BAGHDAD — A series of bomb blasts ripped through one of the holiest cities in Shiite Islam on Sunday, killing at least 10 people in a community still reeling from a deadly bus hijacking earlier this month that left Iraq's Shiites again feeling hunted.

Four explosions struck the city of Karbala over a five-minute period, government officials said, sending thick black smoke over the city. Two of the bombs targeted an Interior Ministry office that issues ID cards. Another struck near a house, shredding its walls and ceiling. And one of the explosions went off half a mile from an important gold-domed shrine.

Prime Minister Nouri al-Maliki, a Shiite, called the bombings a "heinous crime" and warned Iraqis not to be drawn back into sectarian revenge killings.

Ferocious bombing attacks by Sunni insurgent groups like al-Qaida in Iraq targeted the Shiite community, whose leaders came to power after the fall of Saddam Hussein. The bloodshed pushed the nation to the edge of civil war.

Violence in Iraq has fallen dramatically since the bloodletting of 2006 and 2007, but extremist attacks still appear aimed at reigniting the nation's volatile ethnic and religious divide.

The Sept. 12 bus attack targeted Shiite pilgrims from Karbala who were headed to a shrine in neighboring Syria.

The gunmen stopped the bus at a fake checkpoint in the western desert of Anbar province, heavily populated by Sunnis and once one of the heartlands of the insurgency.

The assailants pulled 22 men from the bus and shot them execution-style, leaving the women and children weeping beside a remote highway.

Al-Maliki has been trying to tamp down tensions between officials in Karbala and Anbar since the hijacking. Four suspects are being held in the case, and al-Maliki's military advisers say at least some foreigners were among the plotters.

Sunday's bombings in Karbala were meant to raise tensions further, officials said.

"The aim of these explosions is to ignite the sectarian sedition after the killing of 22 Karbala residents in the Anbar desert two weeks ago," said provincial councilman Hussein Shadhan al-Aboudi. "They also aim to destabilize the security situation in Karbala."

Raed al-Assali, a government employee in the Karbala Investment Council, said there are growing tensions and fear among Karbala residents that they are being targeted by Sunni insurgents.

"There's a feeling here that some groups are trying to ignite sectarian sedition by targeting Karbala after the crisis with Anbar," he said, referring to the slaying of the pilgrims.

Karbala, located 55 miles south of Baghdad, is one of the holiest cities in Shiite Islam because two early Muslim leaders, Imams Abbas and Hussein, are buried there.

The bus attack alarmed Iraqi and U.S. security officials, who are uneasily watching to see if stability will plummet while the U.S. military continues withdrawing from the country. Under a 2008 security agreement, all U.S. troops are required to be out of Iraq by the end of the year.

But concerns about leaving behind partially trained Iraqi forces have spurred Washington and Baghdad to reconsider the deadline, although no agreement has been reached to keep U.S. troops in Iraq beyond 2011.