The explosion ruptured water pipes, flooding streets already soaked by a rare rainstorm, and cut the city's sporadic supply of electricity. The blast damaged buildings along a street that still bore scars from intense fighting between U.S. forces and a Shiite militia in August. For hours afterward, the site was cloaked in a haze of debris and smoke. Workers were still trying to pull bodies out of the wreckage into the evening, said Maj. Ghalib Jazaeri, the Najaf police chief.
There was no immediate claim of responsibility for either attack. But in recent days, Iraqi officials had received reports of insurgents headed from Fallujah to Najaf, near the Euphrates River about 45 miles southeast of Karbala.
U.S. and Iraqi officials have warned of a surge in violence ahead of the Jan. 30 election to choose a 275-member parliament. The Shiite religious leadership has sought to mobilize the community before the vote, seeing it as the best opportunity for long-oppressed Shiites to gain power that reflects their majority status.
Sistani has declared voting a duty, and a committee formed under his auspices negotiated an electoral list known as the United Iraqi Alliance that many expect to be the front-runner among 100 groups and individuals competing in the campaign.
But powerful groups among Iraq's Sunni minority, long the power brokers in the country, have urged a boycott, viewing the election as impossible as long as bloodshed continues, or illegitimate in the shadow of the U.S. military presence. The most militant groups have threatened to attack polling stations, candidates and voters.
"I swear to God, even if they burn all the elections centers, we will still go and vote," said Ali Waili, 29, a taxi driver reached by telephone in Karbala. "We have been mistreated for a long time, we have been tortured for a long time."
In the wake of the attacks, leading Shiite figures appealed for calm. The movement of Moqtada Sadr, a young cleric whose Mahdi Army militia has twice led uprisings against U.S. forces, condemned the attack and dismissed the prospect of sectarian strife.
"It is clear that there are some trying to impose conflict and civil war in Iraq," said Ali Yassiri, a top aide to Sadr. "Deceiving Iraqis is difficult. . . . These attacks will result in nothing but insistence on proceeding toward the Iraq of the future."
Ayatollah Mohammed Saeed Hakim, who with Sistani is one of the country's four most important clerics, called the bombing an attempt to "incite sectarian sedition."
A similar call for restraint was heard at the Ibn Taimiya Sunni mosque in Baghdad, which was struck by at least two mortar rounds at 7 a.m. Four guards were wounded, one of them seriously; windows were shattered and wood paneling was damaged.
Those responsible "must be trying to incite sectarian strife, but this will not happen," said a mosque caretaker, Ali Mashhadani.
The attack on the election commission workers in Baghdad occurred on Haifa Street, a busy downtown thoroughfare. About 30 militants throwing hand grenades and firing machine guns attacked the car as the employees headed to work, the commission said.
The street is one of the city's most notorious. For a time, black banners of the movement of Abu Musab Zarqawi, a Jordanian militant, hung over the street. Along with the banners were uniforms of the Iraqi National Guard -- a warning against Iraqis taking part in the country's fledgling security forces. The inability to control the street has proved a persistent source of frustration for the U.S. military and the interim Iraqi government.
The car was carrying five commission workers, two of whom escaped, said Adel Alami, a commission director. Witnesses quoted by the Associated Press, whose employee took photos of the attack, said insurgents opened fire on the vehicle before dragging people from it and forcing them to kneel in the street. The gunmen punched one of the men and then shot all three at point-blank range. The car was set on fire and the bodies left near the burning wreckage.
Alami acknowledged the threat to the commission's workers but said it was doing everything it could to protect them.
"We do what we can do," he said.
Shadid reported from Baghdad. Special correspondents Omar Fekeiki, Naseer Nouri and Khalid Saffar in Baghdad contributed to this report.