BAGHDAD, Iraq (CNN) -- Iraq's government imposed a weekend curfew in Baghdad on Thursday amid clashes between government troops and Shiite militia fighters, and U.S. Embassy staff were told to remain indoors after days of rocket attacks left two U.S. government employees dead.
Smoke rises after a mortar attack as U.S helicopters fly over the International Zone in Baghdad on Thursday.
The curfew, which took effect at 11 p.m. Thursday (4 p.m. ET), bans pedestrian, motorcycle and vehicle traffic through 5 p.m. Sunday, said Gen. Qassim Atta, an Iraqi military spokesman.
Sixteen rockets were fired Wednesday and 12 on Tuesday. U.S. Embassy workers in Iraq were told to remain in secure buildings and wear protective clothing as rockets continued to rain down on Baghdad's International Zone.
Also called the Green Zone, the International Zone is a heavily fortified central Baghdad district housing the U.S. Embassy and Iraqi government offices.
A senior U.S. official says the insurgents may have had recent training allowing them to conduct more precise targeting of the rockets, believed to be made in Iran. Watch a report on the rockets and their origins »
Meanwhile, the name of the U.S. government official killed in the attacks Thursday has not been released, an Embassy spokesman said.
Another U.S. employee, Paul Converse, died Wednesday from wounds he sustained Sunday, officials said.
And a U.S. soldier was killed by a roadside bomb in eastern Baghdad on Thursday, the U.S. military reported.
Iraq's parliament called a special session for Friday to address the crisis caused by three days of fighting between government troops and Shiite fighters. Meanwhile, Shiite cleric Muqtada al-Sadr called for an end to attacks on his followers.
Fighting between Iraqi government troops and what officials call rogue or outlaw members of Shiite militias has spread through southern Iraq's Shiite heartland to Baghdad since the launch of a government crackdown in Basra on Tuesday.
Three days of fighting have left more than 100 Iraqis dead.
Casualty figures from Basra weren't available Thursday, but the number of deaths is expected to rise from the 40 to 50 reported Wednesday.
The fighting threatens to unravel a seven-month cease-fire by al-Sadr's Mehdi Army. Watch how militias send a message to al-Maliki »
Al-Sadr issued a statement Thursday urging "all groups to adopt a political situation and peaceful protest and to stop shedding the Iraqi blood," according to a senior member of his movement.
Prime Minister Nuri al-Maliki, who has been overseeing the operation in southern Iraq, has ordered militants to surrender their weapons by Saturday.
In Washington, U.S. State Department official Richard Schmierer said the rocket attacks appear to be coming from fighters affiliated with al-Sadr who were "trying to make a statement" about the government offensive in Basra.
Schmierer, the State Department's director of Iraq affairs, discounted the prospect that the cease-fire was collapsing. He blamed the violence on "marginal extremist elements" who have associated themselves with the Sadrist movement.
Iraq's Interior Ministry said mortar rounds killed one person and wounded four in the city's central Karrada district on Thursday evening, and the ministry's own compound was hit by one shell, wounding seven police officers.
Also Thursday in Baghdad, dozens of gunmen kidnapped the spokesman for the Baghdad security plan, Tahseen Sheikhly. Three of his guards were killed and his house burned in the attack, which an Interior Ministry official said was carried out by "outlaws," a reference to al-Sadr's militia.
A car bomb killed three people and wounded five others near a police patrol in central Baghdad on Thursday, an Interior Ministry official said. There are no apparent links to the violence in the Shiite regions.
People in Basra report smoke rising and gunfire and explosions ringing out across the city. Iraqi security forces, backed by U.S. and British troops, have been taking on fighters using grenades, mortar rounds and machine guns.
A Basra provincial official said on condition of anonymity that weapons such as machine guns and grenades were stolen from a military post in the Muqal area.
Al-Maliki briefed city and provincial officials Wednesday about the offensive and vowed to finish the job.
Provincial officials expressed reservations about the operation, saying Basra will fall into the hands of "outlaws" if al-Maliki fails to restore order.
Basra has been relatively quiet during the war, but the southern city has seethed with intra-Shiite tensions as Sadrists, the Islamic Supreme Council of Iraq and the Fadhila party have jockeyed for power. Learn more about the major players »
Much of the fighting in the Shiite heartland involves followers of al-Sadr and security forces aligned with the Islamic Supreme Council of Iraq's militia, the Badr Brigade.
The council dominates the ruling United Iraqi Alliance, but the Sadrist movement left the government last year after al-Maliki refused to demand a timeline for the withdrawal of American forces from Iraq. Both groups have strong contingents in the Iraqi parliament.
A provincial council official also said insurgents sabotaged an oil pipeline Thursday in Zubeir, a town near Basra. The attack sparked a large fire on the pipeline, which transfers crude oil to tanks in the city.
Meanwhile, the FBI identified the remains of two U.S. contractors who had been missing in Iraq for more than a year, a bureau spokesman said Thursday.
Minnesotan Paul Johnson-Reuben, 41, and Californian Joshua Munns, 25, were among four men kidnapped in November 2006 during an ambush in the southern Iraqi town of Safwan. All four worked for the Crescent Security Group, a Kuwaiti-based firm that escorts convoys.
The other two men -- Jonathon Cote, 25, and Bert Nussbaumer, 26 -- are still listed as missing. The FBI has the remains of one more body, which the bureau is trying to identify. E-mail to a friend
CNN's Mohammed Tawfeeq and Jonathan Wald contributed to this report.