One U.S. soldier was killed and six others injured when rocket-propelled grenades were fired at a military convoy traveling in Baghdad (search), U.S. Central Command said Monday.

The soldiers were with the 3rd Infantry Division (search), which is charged with patrolling the Iraqi capital, said Spc. Giovanni Llorente, a military spokesman. The attack occurred around 6 a.m. as another U.S.-led anti-insurgency operation was well under way, and just hours after the U.S. defense chief warned attacks against Americans in the postwar nation were likely to continue.

At least four suspected loyalists were killed and big weapons caches were captured in the latest operation, called Ivy Serpent, which aims to blunt potential anti-American attacks ahead of now-banned holidays of Saddam's Baath Party (search).

Centcom did not provide details on the deadly attack against U.S. forces in Baghdad, but there were several explosions along the al-Khadra Highway in western Baghdad early Monday, and an Associated Press photographer on the scene said witnesses reported U.S. casualties. It was not clear if it was the same incident referred to by the military.

Meanwhile, the military announced that one soldier was killed and two others injured early Sunday when a tractor trailer crashed accidentally into their vehicle, parked at a checkpoint outside a base in Diwaniyah, 100 miles south of Baghdad. The names of the soldiers were withheld pending family notification.

Also Sunday, Iraqi police and coalition forces exchanged fire at a military checkpoint in Baghdad, witnesses said. They said a police vehicle drove up to a coalition checkpoint and started shooting, and U.S. soldiers returned fire. It was not clear if there were casualties, and the U.S. military had no immediate comment.

U.S. forces also detained nine "high-value targets" in raids near Mosul, in northern Iraq, none of them on the list of 55 most-wanted Iraqis from Saddam's old regime.

Ivy Serpent, launched late Saturday in Sallahadin and Diala provinces, has so far yielded over 50 detainees in about a dozen raids before key holidays supported by Saddam loyalists. The four suspected anti-American militants were killed when they opened fire on Army scouts near Baqouba, military officials said.

The Army said insurgents planned a series of attacks against U.S. soldiers to commemorate the July 14, 1958, overthrow of Iraq's King Faisal and the July 17, 1968, Baath Party coup.

"We want to get within the enemy's temple, disrupt his timing," said Col. David Hogg, commander of 4th Infantry Division, 2nd Brigade.

The July 17 holiday was one of six banned Saturday in the first action of Iraq's new government council, which also named a national holiday marking Saddam's ouster.

Defense Secretary Donald H. Rumsfeld warned Sunday that attacks on U.S. troops in Iraq may worsen this summer. "There's even speculation that during the month of July, which is an anniversary for a lot of Baathists events, we could see an increase in the number of attacks," Rumsfeld said on NBC's Meet the Press.

At least 31 U.S. soldiers have been killed in hit-and-run small-arms assaults in Baghdad and central Iraq since President Bush declared major fighting over May 1. In response, the army has launched a series of high-profile operations — Peninsula Strike, Desert Scorpion, Sidewinder and now Ivy Serpent — to crush the insurgency.

The operations have been complex, high-tech nighttime affairs and have produced mixed results.

In Saturday's night raids, AC-130 gunships flew over the sites, as Apache and Kiowa helicopters hovered. Tanks established security cordons, and Humvees and Bradley fighting vehicles carrying infantrymen stormed houses and walled compounds. Unmanned aerial reconnaissance vehicles gave commanders and tacticians at headquarters a bird's-eye view of the action.

In some raids, U.S. forces acted on specific intelligence and detained many suspects.

In the village of Mutlaq Nayif, just north of Taji along Highway 1, loudspeakers ordered residents to get out of their homes. After searching the tall grass surrounding the homes, soldiers walked out with armfuls of assault rifles, machine guns, stocks of ammunition, camouflage military uniforms and the black robes used by Fedayeen warriors. Col. Frederick Rudesheim, commander of the 4th Infantry Division 3rd Brigade, said 35 people were detained.

In the Tigris River town of Hassan bin Mahmud, which Rudesheim described as "the village that time forgot," a monument to Saddam remained standing in the town square. Locals cursed arriving American soldiers, said Rudesheim, whose men blew up the statue of the ousted Iraqi leader.

In Muqtaria, north of Baquba, a group of armed men fled into fields as the Americans approached. Soldiers searched the area, ultimately detaining 10 men. "It was a cat and mouse game all night," Hogg said.

Near Balad, servicemen found two anti-aircraft guns which they destroyed. Near Baqouba, soldiers raided two houses producing anti-American propaganda. They captured a former general in Saddam's Fedayeen militia, a former air force general and the former number two in the Diala province Baathist party. All are suspected of organizing anti-U.S. violence.

The Associated Press contributed to this report.