BAGHDAD, Iraq, AP – A suicide car bomber slammed into a U.S. Marine convoy west of Baghdad and there were casualties, the military said Friday. A top U.S. commander testified before Congress that the foreign fighter problem in Iraq has worsened.

The attack happened Thursday night in Fallujah, 40 miles west of Baghdad. The troops were assigned to the II Marine Expeditionary Force, the military said. No further information was made available.

Separately, American and Iraqi troops battled al-Qaida-linked insurgents holed up in a house in an upscale part of Baghdad Thursday, killing at least five militants apparently waiting to carry out suicide bomb attacks.

Word emerged that a senior al-Qaida leader was killed in a U.S. airstrike near Syria”s border. And in a devastating escalation in insurgent attacks in the capital, a string of car bombings carried over into Thursday morning with four more blasts that killed at least 15 people and wounded 28.

Among the wounded was a young boy, his left leg missing from below the knee, who sat on the sidewalk near a mangled bicycle, screaming as a man called for help.

The force of the blasts — timed for when the capital”s streets are most crowded — blew off store shutters, and the surrounding sidewalks were littered with debris, including charred vegetables and fruit.

Overall, Thursday”s violence across Iraq left at least 20 civilians killed and 37 wounded.

The bloodshed underscored comments from the top American commander in the Persian Gulf, who told Congress the Iraqi insurgency has not grown weaker over the past six months.

&#34I believe there are more foreign fighters coming into Iraq than there were six months ago,&#34 Gen. John Abizaid said.

Defense Secretary Donald H. Rumsfeld told the same panel in Washington that Iraq”s own security forces have &#34a way to go&#34 before they are ready to take over the job from U.S. forces, adding that he opposes congressional calls for a timetable for withdrawing American troops.

Foreign fighters, mostly from Iraq”s Arab neighbors, are thought to be responsible for many of the car bombings that have killed thousands of Iraqis over the past 18 months.

Iraq”s shared border with Syria is named as the main point of infiltration. On Thursday, Secretary of State Condoleezza Rice pressed Syria again to follow through on a pledge to secure its border with Iraq.

But in Damascus, Syrian Foreign Minister Farouk al-Sharaa said Syria will ask Baghdad to provide evidence of militants infiltrating across their shared border. He also said a Syrian delegation will soon go to Baghdad to discuss restoring diplomatic ties, severed in 1982.

Thursday”s gunbattle erupted in western Baghdad”s al-Jamaa neighborhood, where Sunni and Shiite professionals live. The house caught fire and then exploded during the gunbattle, the military said.

Afterward, dozens of residents gathered as U.S. troops loaded one Humvee with heavy machine-guns, rocket-propelled grenades, rifles and belts of ammunition found inside. Iraqi police put bodies onto a pickup truck.

The insurgents were associated with Abu Musab al-Zarqawi, head of al-Qaida in Iraq, the military said.

The U.S. military said six insurgents were killed. Al-Qaida in Iraq said five of its men, four foreign Arabs and one Iraqi, were in the house waiting for &#34their turn to leave the world,&#34 a reference to suicide bombings.

It said the five men &#34used all kinds of weapons&#34 to keep the attackers at bay, forcing them to retreat with huge losses.

&#34The crusaders, as usual when they lose, called for the warplanes which bombed the house and the five joined the martyrs,&#34 it said in a statement posted Thursday night on a militant Internet site. Its authenticity could not be independently verified.

An al-Qaida affiliate, the Ansar al-Sunnah Army, claimed responsibility for a series of car bombs that killed dozens of Shiite Muslims over a 12-hour span in Baghdad. The bombings appeared designed to stoke sectarian tensions and push the country into civil war.

In an Internet statement posted Thursday, al-Zarqawi said Abdullah Mohammed Rashid al-Roshoud was killed in a U.S. airstrike during fighting with U.S. and Iraqi forces. The campaign took place last weekend near the Syrian border in northwest Iraq.

Al-Roshoud, a Saudi, had been No. 24 on a list of the 26 most-wanted terrorist leaders issued by Saudi Arabia two years ago — and was one of only three at large. The statement did not say when he was killed, but U.S. warplanes carried out numerous airstrikes during an operation that targeted foreign fighters being smuggled into Iraq from Syria.

The bloodshed has left more than 1,240 people dead since April 28, when Prime Minister Ibrahim al-Jaafari announced his Shiite-dominated government.