BAGHDAD - U.S. forces stepped deeper Friday into the Iraqi government's fight to cripple Shiite militias, launching airstrikes in the southern city of Basra and firing a Hellfire missile in the main Shiite stronghold in Baghdad.
The American support occurred as Iraqi troops struggled against strong resistance in Basra and retaliation elsewhere in Shiite areas — including more salvos of rockets or mortars into the U.S.-protected Green Zone in Baghdad.
It was the first time American jets have been called to attack militia positions since Iraqi ground forces launched an operation Tuesday to clear Basra of the armed groups that have effectively ruled the streets of the country's second-largest city for nearly three years.
One militia barrage slammed into the headquarters of the Basra police command late Friday, triggering a huge fire and explosions when one of the rounds struck a gasoline tanker, police officials said.
Earlier Friday, U.S. jets struck a building housing militia fighters and blasted a mortar team that was firing on Iraqi forces, British military spokesman Maj. Tim Holloway said without further details.
Many of those groups are believed to receive weapons, money and training from nearby Iran, the world's most populous Shiite nation.
The crackdown in Basra has provoked a violent reaction — especially from the Mahdi Army of anti-American Shiite cleric Muqtada al-Sadr. His followers accuse rival Shiite parties in the government of trying to crush their movement before provincial elections this fall.
Their anger has led to a sharp increase in attacks against American troops in Shiite areas following months of relative calm after al-Sadr declared a unilateral cease-fire last August.
Before dawn Friday, a U.S. aircraft fired a Hellfire missile in the Sadr City district — the Baghdad stronghold of the Mahdi Army — after gunmen there opened fire on an American patrol.
The U.S. military said the missile strike killed four militants, but Iraqi officials said nine civilians were killed and nine others wounded.
Another U.S. airstrike targeted a rocket-propelled grenade mounted vehicle in the mostly Sunni neighborhood of Azamiyah, killing two militants, the military said separately.
Defying a curfew in Baghdad, Shiite extremists lobbed more rockets or mortars against the U.S.-protected Green Zone, which has come under steady barrages this week. The attacks prompted the State Department to order embassy personnel to stay inside.
At least two rounds Friday struck the Green Zone offices of Sunni Vice President Tariq al-Hashemi, killing two guards and wounding four, his daughter and executive secretary Lubna al-Hashemi said.
In all, the U.S. military said 13 suspected militants were killed Friday and 26 on Thursday in Baghdad operations.
"As you know, we've been getting attacked and going after the enemy all day," said Maj. Mark Cheadle, a spokesman for the Baghdad area command.
An American soldier was fatally injured Friday in a roadside bombing south of Baghdad, the military reported without elaboration. The area is religiously mixed, and it was unclear whether he was killed in a Shiite district.
At least 26 people were killed Friday in fierce fighting in the southern cities of Mahmoudiya, Nasiriyah and Kut, according to police and army officials who spoke on condition of anonymity because they weren't authorized to release the information.
Prime Minister Nouri al-Maliki, a Shiite who once maintained close ties to al-Sadr, has put his personal prestige on the line in the Basra crackdown, flying to the city five days ago to assume personal command of the operation there.
Al-Maliki has vowed there would be "no retreat" in Basra, the nation's commercial center and headquarters of the vital oil industry.
In Washington, President Bush said the battle against Shiite extremists presents "a defining moment in the history of Iraq" and a "necessary part of the development of a free society."
The United States has called the Basra campaign an important test of Iraq's ability to handle its own security affairs. But setbacks in the battle could increasingly draw in American forces, worried that a sustained fight — and the backlash in Baghdad and elsewhere — could wipe away many of the security gains of recent months.
The situation in Basra remained tense as a Friday deadline for gunmen to surrender their weapons and renounce violence expired, although a few complied. Al-Maliki's office announced a new deal, offering Basra residents unspecified monetary compensation if they turn over "heavy and medium-size weapons" by April 8.
Masked militia fighters, meanwhile, moved around freely in a southwestern neighborhood and there was little traffic, according to Associated Press Television News footage. Residents complained of rising food prices and power shortages.
The government relaxed a days-old curfew in Basra to allow people to move around in the city from 6 a.m. to 6 p.m. to facilitate shopping and other necessary tasks.
"The situation was better this morning so I went to a small market near my house. I was surprised that the price of vegetables and meat had gone up fivefold," said Ziyad Khalid, 27.
Hamid Saaid, 47, said he saw dozens of people lined up for bread and to fill canisters with clean water from a tanker truck.
In Baghdad, the Sunni speaker of Iraq's parliament called a special legislative session Friday in hopes of launching an initiative to negotiate a peaceful end to the Basra fighting.
But the main Shiite political bloc, the United Iraqi Alliance, and its Kurdish allies refused to attend. The alliance includes al-Maliki's party and the Supreme Islamic Iraqi Council, the main political rival to al-Sadr's movement.
With so few lawmakers attending, parliament could approve no binding resolutions but instead established a committee to explore ways to mediate a settlement. The initiative was spearheaded by former prime minister Ibrahim al-Jaafari, who brought al-Sadr's followers into the government under his administration.
Al-Maliki has insisted the fight is targeting criminal gangs in Basra, not al-Sadr's movement.
However, al-Sadr's followers sharply condemned the prime minister during sermons Friday in mosques across the country.
"He imprisoned and displaced thousands of Iraqi people under the name of democracy. He is killing the citizens in the south of Iraq," Sheik Jalil al-Sarghi said, referring to al-Maliki as U.S. helicopters buzzed over the office where the prayer service was held.
Associated Press writers Qassim Abdul-Zahra and Saad Abdul-Kadir contributed to this report.