Elsewhere, U.S. troops clashed with rioters carrying Saddam's picture Friday in a Baghdad suburb, and a heavy smoke billowed from the mayor's office in a city west of the capital following a strong explosion.
An upsurge of attacks this week, coinciding with the start of the Muslim holy month of Ramadan, has killed scores of people, most of them Iraqis who died in a series of vehicle bombings in Baghdad on Monday. The upsurge prompted the international Red Cross and the United Nations to remove foreign staff temporarily.
The New York Times reported Friday that senior U.S. officials believe the former Iraqi leader, who has been on the run since U.S. forces took over Baghdad in April, is playing a major role in coordinating and directing attacks against American troops.
The suspicion of Saddam's involvement is the latest theory on who is directing the attacks that have killed 117 American soldiers since the end of major combat was declared on May 1.
Earlier this week, U.S. officials suspected a top Saddam aide was leading the resistance along with the terror group Ansar al-Islam. President Bush blamed Baathists and foreign terrorists for recent terrorist bombings. A senior U.S. counterterrorism official said Thursday that al Qaeda might be behind Baghdad attacks this week.
In other developments:
Starting around midnight Thursday, U.S. soldiers moved into Saddam's home village, erected barbed wire fences, took up positions in dugout holes and established checkpoints on the road leading in and out of the village of about 3,500 residents. All cars were stopped and searched and people on the road were questioned about their identity.
Lt. Col. Steve Russell, commander of the 1st Battalion, 22nd Infantry Regiment of the 4th Infantry Division, said he did not know whether Saddam was directing parts of the insurgency, but the village is the family home of many former Baathist regime members.
"There are ties leading to this village, to the funding and planning of attacks against U.S. soldiers," Russell said.
All persons over the age of 18 would register with the coalition forces and receive identity cards that will allow them to move in and out of the village, U.S. officers said.
By morning, dozens of men from Uja had lined up outside the local police station, waiting to give personal data and have their picture taken for a computer-made ID card.
"I chose right in coming here. We need the safety," said Ahmed al-Naseri, a father of three children, who said he was a cousin of Saddam.
"We need freedom," he added while waiting in line.
The Times, citing unidentified senior officials, said recent intelligence reports have portrayed Saddam as a catalyst or even a leader in the armed opposition, probably from a base of operations near his hometown of Tikrit. The reports have not been corroborated, one official told the newspaper.
In a speech Thursday night, Rumsfeld said attacks are practically inevitable as long as Saddam remains on the loose.
"The fact that he's alive is unhelpful," Rumsfeld told the conservative think tank Empower America. "We do need to catch him and I think we will."
Whether its Saddam, al Qaeda, or another party, the attacks troops are increasing in sophistication. Before Monday, bombers in Iraq had largely used relatively crude devices cobbled together from old Soviet-era munitions.
But each of the vehicles used in the latest attacks, which targeted the International Red Cross headquarters and four Iraqi police stations, was packed with 1,000 pounds of plastic explosives, the official said. A fifth bomber was prevented by police from detonating his device and was taken into custody.
In Baghdad, the clash at Abu Ghraib, a suburb on the western side of the capital, broke out when U.S. troops tried to clear market stalls from a main road. Youths began throwing stones and troops and Iraqi police and set tires ablaze.
Protesters carried Saddam's picture and shouted "Allahu Akbar," or "God is great."
After a three-hour interlude, gunfire erupted again as U.S. tanks moved into the area. Ten explosions were heard, and fleeing civilians said the U.S. troops had "come under attack." Within a half hour the gunshots subsided.
In Fallujah, a center of Sunni Muslim resistance 40 miles west of the capital, a strong explosion rocked the center of the city at midday. Heavy block smoke could be seen billowing from the mayor's office.
Police said that following the explosion, residents shouted at the authorities that their neighborhood had become a target because the U.S.-appointed mayor and other officials worked there. Civil defense officer Ahmed Khalil said police shot dead a resident during the ensuing argument.
Elsewhere, insurgents mounted a series of harassing attacks on U.S. and Iraqi government targets in the northern city of Mosul, U.S. officers said Friday. There were no injuries in the overnight shelling of a U.S. base near Mosul, the explosion of a roadside bomb near a U.S. foot patrol on the city's outskirts, or in an attack by unidentified gunmen who sprayed Mosul's city hall with automatic fire, they said.