Insurgents launched two deadly attacks Friday in Baghdad (search), killing an American soldier and wounding a civilian contractor in a mortar barrage on a U.S. base, and injuring three U.S. troops in a coordinated ambush in another part of the capital.

The attacks were among several in Sunni Muslim (search) areas of Iraq following a series of deadly car bombings this week that have unnerved an Iraqi public before the transfer of sovereignty at the end of this month.

Three Iraqi civilians died in the ambush, which began when a roadside bomb exploded in the Kamalaya district of east Baghdad, the U.S. command said. Insurgents opened fire from the rooftops. U.S. troops returned fire and the insurgents "sustained moderate casualties," the statement said.

Several hours later, six mortar shells exploded at a 1st Cavalry Division camp in southern Baghdad, killing an American soldier and slightly injuring a contractor working for Kellogg Brown and Root (search), the military said.

Elsewhere, American soldiers clashed with insurgents Friday for a second straight day in the Sunni town of Buhriz outside Baqouba, 35 miles northeast of Baghdad.

Insurgents also attacked U.S. troops Friday at a police station in the Sunni Triangle city of Samarra, firing rocket-propelled grenades and rifles after warning shopkeepers to close, witnesses said. U.S. troops returned fire, wounding two attackers, residents said by telephone. There was no report on U.S. casualties.

In the south, British soldiers traded small arms fire overnight with Shiite fighters loyal to radical cleric Muqtada al-Sadr in Amarah, witnesses said. There were no British casualties but two insurgents were killed.

A coalition spokesman said the smaller of two oil pipelines blasted by insurgents this week had nearly been repaired, although engineers were still examining the larger one.

Spokesman Dominic d'Angelo said tests could begin on the smaller pipeline Saturday but full exports would probably not resume before June 16. Iraqi exports were suspended Wednesday because of the attacks on the pipelines, which carry crude oil from the southern fields to tankers in the Gulf.

Exports from Iraq's other field near Kirkuk were halted last month due to sabotage on the pipeline to the Mediterranean port of Ceyhan, Turkey.

The attacks against the pipeline were part of a stepped up campaign of violence in the run-up to the June 30 transfer of sovereignty to the interim Iraqi government. The attacks appear aimed at undermining public confidence as the date approaches.

In the boldest attack in months, a car bomber smashed into a crowd seeking jobs at a military recruitment center Thursday in Baghdad, killing at least 35 Iraqis and wounded another 145. Another car bombing the same day killed six Iraqi civil defense fighters and injured four others in Balad, north of Baghdad.

The coalition deputy operations chief told Associated Press Radio that Iraqis themselves must step forward and provide information on the insurgents if the Americans and their Iraqi and international partners are to halt the violence.

"The sooner we get every person in this country understanding their responsibility to provide us intelligence on those people in their neighborhoods who they believe to be participating in these attacks," the sooner they will stop, Brig. Gen. Mark Kimmitt said Friday. "We need to get that intelligence from them so we can pre-empt these attacks before they happen."

He said U.S. forces were "working hard to try to develop the intelligence to find these people" responsible for the violence "so we can nip these attacks in the bud."

The fighting in Buhriz near Baqouba began Thursday when insurgents fired on a 1st Infantry Division patrol. Ten insurgents were killed and one American soldier was wounded in the ensuing firefight, division spokesman Maj. Neal O'Brien said.

Fighting resumed Friday when another patrol came under fire in Buhriz. At least five insurgents were killed, O'Brien said. There were no U.S. casualties. Fighting persisted intermittently throughout the day, witnesses said.

In an afternoon clash, insurgents wearing red scarves blasted a U.S. patrol with machine gunfire and RPGs as the Americans tried to enter the market district.

"We are ready to defend our city against the invasion by the occupiers," one youthful fighter said, refusing to give his name. Electricity was cut off in the city due to power lines damaged in the clashes.

In the Shiite city of Kufa, al-Sadr denounced interim President Ghazi al-Yawer as an American-installed puppet.

"Your alliance with the occupation will bring only shame and disgrace to you," al-Sadr told al-Yawer in comments read by an aide during the weekly Friday sermon at the Kufa mosque.

Al-Sadr's uprising, launched in April after U.S. occupation authorities closed his newspaper, has left hundreds dead in clashes with U.S. troops, although the rebellion has largely petered out.

Al-Sadr said he was "hurt" to see al-Yawer shaking hands with President Bush on the sidelines of the G-8 summit in Sea Island, Ga., last week. Al-Sadr called the visit "a sign of weakness."

Al-Yawer, a Sunni Muslim, has encouraged al-Sadr to transform his al-Mahdi Army into a political movement and compete for power in the January elections. The United States had vowed to "capture or kill" al-Sadr but now appears willing to let Iraqi authorities deal with him.