BAGHDAD, Iraq - U.S. and Iraqi forces pushed deeper Thursday into Sunni militant strongholds in Baghdad - where cars rigged with explosives greeted their advance - while British-led teams in southern Iraq used shipping containers to block suspected weapon smuggling routes from Iran.
The series of car bomb blasts, which killed at least seven civilians, touched all corners of Baghdad. But they did little to disrupt a wide-ranging security sweep seeking to weaken militia groups' ability to fight U.S.-allied forces - and each other - as Iraq slips further into factional bloodshed.
The attacks, however, pointed to the critical struggle to gain the upper hand on Baghdad's streets. The Pentagon hopes its current campaign of arrests and arms seizures will convince average Iraqis that militiamen are losing ground. Yet each explosion is another reminder of the militants' resources and resolve.
Most of the latest resistance has come from Sunni factions, which perceive their Saddam Hussein-era influence slipping away as the majority Shiites extend their political muscle and bolster ties to powerful Iran.
In Baghdad's Dora neighborhood - a longtime Sunni militant hotbed - two parked cars wired with explosive were triggered as a joint U.S.-Iraqi patrol rolled pass. The convoy was unharmed, but the blast killed at least four civilians and injured 15.
Control of the Dora district, a once upscale neighborhood favored by Saddam's regime favorites, is important as a gateway between Baghdad and the Iraq's Shiite-dominated south. Two other car bomb blasts came as security forces moved through the city, killing at least three civilians.
Outside Baghdad, troops also faced Sunni ambushes. In Buhriz, about 30 miles northeast of Baghdad, Sunni gunmen and soldiers from the 1st Squadron, 12th Cavalry Regiment engaged in a 20-minute firefight.
U.S. Bradley fighting vehicles fired 25mm rounds into homes shielding the gunmen, said an Associated Press reporter traveling with the unit.
No U.S. casualties were reported and the militant toll was not know.
Even the first steps of the security operation display the sectarian divides complicating any plan to calm Baghdad - which is key to begin stabilizing the rest of the country.
A leader of the main Sunni bloc in parliament, Adnan al-Dulaimi, claimed the U.S.-led sweeps have "started to attack" mostly Sunni areas. "It should concentrate on those who perpetrating the violence and terrorist acts in all districts," he said - an apparent reference to the Shiite militia stronghold of Sadr City.
Around the city, U.S. and Iraqi soldiers set up dozens of roadway checkpoints and conducted top-to-bottom searches of vehicles and motorbikes. Waiting in a snarl of traffic at one blockade, Mohammed al-Jubouri said people are willing to put up with the troubles as long as the latest security sweep shows some results after a wave of bombings have killed hundreds of civilians since the beginning of the year.
"We are fed up with these stalling words," he said. "We want only the security and stabilization."
Mohammed Ali Jassim, a 40-year-old Sunni owner of a spare parts store, said he was hopeful it would work after he was forced to abandon his business in Sinak, one of Baghdad's commercial areas where more than 50 people were kidnapped by gunmen disguised in military uniforms late last year. Jassim's brother was among the victims.
"I wish I could open my store again and send my children to their schools without fear of being kidnapped or killed," said Jassim.
But a supermarket owner in western Baghdad, Anwar Abdullah, claimed the security push is doomed for failure because most of the militants have fled the city in advance.
"It sounds that we are going to be affected more than terrorists by this security plan," he said.
After nightfall - and the daily citywide curfew - U.S. warplanes flew low over Baghdad in an apparent attempt to show the security push is gathering momentum.
In southern Iraq, British and Iraqi security forces closed two border points with Iran at Sheeb and Shalamcha - blocking the gates with large metal shipping containers - and expanded coastal patrols to monitor maritime traffic into southern Iraq, a statement said.
Authorities also set up checkpoints ringing Basra, Iraq's second-largest city and the commercial hub of the Shiite-dominated south. The British military said the operation would last for 72 hours.
U.S. President George W. Bush said Wednesday the Iranian government is providing armor-piercing bomb to kill American soldiers in Iraq, although he backed away from claims the top echelon of Iran's government was responsible.
Iraq also temporarily closed its borders with Syria on Wednesday. Washington and some allies have claimed Sunni militants have used Syria's porous border with Iraq as vital supply routes.
In other developments:
- Another round of conflicting reports deepened the mystery about the whereabouts of radical Shiite cleric Muqtada al-Sadr, whose loyalists include the Mahdi Army militia.
A top adviser to Iraq's prime minister, Sami al-Askari, said al-Sadr traveled to Iran "a few days ago," but gave no further details on how long he would stay. He denied that al-Sadr left the country in fear of arrest under the security crackdown. But a lawmaker loyal to al-Sadr, Saleh al-Ukaili, insisted that al-Sadr is in Iraq and claimed the accounts of his departure were part of a "campaign by the U.S. military" to track down the elusive cleric.
A statement from the office of Iraqi President Jalal Talabani quoted him saying that he has no information on al-Sadr's location, but he believed "many of the Mahdi Army commanders have been instructed to leave Iraq to facilitate the mission of the security forces."
- A U.S. Marine was killed in combat operations in Iraq's western Anbar province, a Sunni militant stronghold. His name was not released pending notification of relatives.