BAGHDAD -- A resurgence of deadly attacks bearing the marks of al Qaeda has created deep concerns among Iraqis barely a month before U.S. troops are largely to withdraw from major cities and towns.
The rash of attacks that began in April has killed more than 400 people and stirred memories of the sectarian bloodletting that nearly plunged the country into all-out civil war in 2006 and 2007.
Apart from al Qaeda, other suspects include members of the 100,000-strong Sunni Awakening movement, which joined American forces during the U.S.-led surge to defeat al Qaeda. Initially given monthly stipends by U.S. forces, thousands of Awakening fighters have gone months without being paid since the Americans gave the Iraqi government responsibility for meeting the payroll.
Another possible factor in the resurgence is the release of tens of thousands of detainees from U.S.-run prisons under the security agreement signed by the two countries last December.
On Iraqi state-run television, Prime Minister Nouri al-Maliki and other government officials have repeatedly blamed what they call a partnership between al Qaeda in Iraq and remnants of the late Iraqi dictator Saddam Hussein's Ba'ath Party.
"This is definitely al Qaeda. This is their style for sure," said Maj. Gen. Jihad al-Jaberi of the Iraqi Interior Ministry, who commands bomb-disposal teams in Baghdad, after assessing forensic evidence left in the charred remains of people and vehicles.
Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said Sunday that the U.S. remained on schedule to withdraw its troops from cities by June 30, when Iraqi security forces are due to take over.
"Their army and their police, in terms of providing for their own security, they've improved dramatically," Adm. Mullen told ABC News.
"Al Qaeda is still active; they're not gone," he said, while noting the recent uptick in violence.
The U.S. military's top spokesman in Iraq, Maj. Gen. David Perkins, agreed that forensic evidence supports known operational patterns of al Qaeda and said arrests have been made at shops where vehicles used in car bombings were fitted with explosives.
One sign of progress, according to Gen. Perkins, is that many of the recent incidents have not been suicide bombings. That suggests fewer foreign fighters are infiltrating Iraq from Syria and other Arab countries.
"When we had some vehicle-borne IEDs [improvised explosive devices], none of them were being driven. They were parked. Someone would drive a car, park it, leave it on a timer - a washing-machine timer, something like that - and then leave the vehicle where it was."
While such car bombings are also deadly, he said they are generally less lethal than suicide car-bombings "because a driven vehicle is, in essence, a guided weapon that can drive into a crowd or a market."
So far, there does not seem to have been any organized retaliation by armed Shi'ite groups for the bombings, which have targeted Shi'ite neighborhoods, markets and mosques.
Most notably absent, at least in comparison with the dark days of 2006 and 2007, are the violent actions of the Mahdi Army, a Shi'ite militia led by cleric Muqtada al-Sadr. After two rather mysterious years of religious study in Iran, the cleric recently surfaced in Turkey and appears to be positioning himself to make a grand comeback to Iraq as a political and religious force.
Abdul-Hadi al-Hassani, a member of parliament from Mr. al-Maliki's Dawa Party, said that "the Shi'ites have limited patience, but what happened lately has proved that they want to prevent Iraq from getting dragged back to the sectarian conflict."
"If this does happen," he added, "it would burn everything. It would take the political process back to zero."
Still, the violence is unsettling. Last Wednesday night in Baghdad's Shula neighborhood, a driver parked on the side of a popular street lined with restaurants and an ice-cream parlor before disappearing among the evening shoppers and diners. The car exploded, sending metal shards and fire through the crowds, killing more than 40 people and injuring more than 70, according to local police.
On the following morning, two more explosions shattered the calm in Baghdad, and a third occurred in the northern city of Kirkuk. At least 25 Iraqis were killed, as were three members of the U.S. military.
In two of the incidents, suicide bombers were to blame. They blended in by wearing the uniforms of Iraqi security forces.
Anthony Cordesman, a national security and Middle East specialist at the Center for Strategic and International Studies in Washington, said, "People throughout the Iraqi security forces have often left their jobs without becoming any kind of insurgent or fighter, but in the process, they sell what they take with them, which includes their uniforms. This makes it extremely difficult to figure out who is in and who is out."
"You could not secure Washington, D.C., against this kind of suicide bombing," Mr. Cordesman added. "You could protect individual facilities, but if people are going to assemble in parks or any other public place, the reality is that every society remains vulnerable."
Gen. al-Jaberi suggested one possible solution. "Since many security forces have been infiltrated by al Qaeda, I have suggested that all checkpoints must be manned by both the Iraqi Army and the local police," he said. "That way, we will watch each other, and will be able to know who is working for the country, and who is working for the bad people."
Yousif al-Timimi contributed to this report.