In Washington, the Pentagon said 18,490 US troops had been wounded in the war, which began in March 2003. On an average day, about two US military personnel are killed.
Tens of thousands of Iraqis have also been killed since the US-led invasion more than three years ago to overthrow Saddam Hussein, igniting an uprising by his once-dominant Sunni Arab minority that is showing little sign of easing.
The US military said it believed the real identity of al-Qaeda's new leader in Iraq is Egyptian-born Abu Ayyub al-Masri and that it expected him to adopt the same methods as his predecessor Abu Musab al-Zarqawi, killed in a June 7 air raid.
On a day when at least 24 Iraqis lost their lives in five separate attacks, an official in Baghdad said the security forces had seized documents giving key information about the militant group's network and its leaders in Iraq.
Mowaffaq al-Rubaie, the national security adviser, said: "We believe this is the beginning of the end of al-Qaeda in Iraq."
Al-Rubaie told Reuters earlier this year the violent campaign against the Iraqi government had been defeated. But violence has continued to rage, killing hundreds of people since.
In Thursday's bloodiest attack, armed men stopped a minibus taking 10 labourers to work in the town of Baquba, forced them to get off and killed them, a police source said.
Reuters Television footage showed the dead men lying on stretchers in blood-soaked clothes. "Is this Islam? Is this Islam?" the father of one victim wailed.
Al-Masri is al-Qaeda in Iraq's new
leader, according to the US Army
Baquba is the capital of Diyala, a religiously mixed province north of Baghdad, that has seen many gruesome attacks.
Further west, attackers opened fire on a Sunni Arab mosque in a small town near Tikrit, Saddam's home city, killing four worshippers and wounding up to 20 others.
In the northern town of Tal Afar, three roadside bombs killed five Iraqi soldiers.
The US has 130,000 troops in Iraq. Bush has resisted setting a timetable for their withdrawal, saying it depends on the situation on the ground. Al-Rubaie said all foreign forces may be gone by mid-2008, as Iraq takes over security.
About 50,000 Iraqi troops, supported by more than 7,000 US-led troops, launched a security crackdown in Baghdad this week aimed at putting further pressure on insurgents.
The challenge in restoring stability was highlighted by a car bomb in front of a bakery that killed at least three people in the southwestern Saydiya district on Thursday.
Analysts say al-Qaeda activists, though behind some of the bloodiest attacks, only make up about 5% of Sunni fighters, which are dominated by Saddam loyalists.
On the attack
"The government is on the attack now ... to destroy al-Qaeda and to finish this terrorist organisation in Iraq," al-Rubaie said.
He said some documents were found in an al-Qaeda hideout where al-Zarqawi had been, but did not make clear whether this was the place where the Jordanian fighter was killed.
A copy of one of the documents, whose authenticity could not be independently verified, did not mention al-Qaeda or give specific information about any planned attacks.
"The government is on the attack now ... to destroy al-Qaeda and to finish this terrorist organisation in Iraq"
Iraq's National Security Adviser
Instead, it suggested ways anti-government fighters could counter US raids and propaganda, for example by infiltrating Iraq's armed forces, recruiting new members and manufacturing more weapons.
It also said the best way to get out of "the crisis" was to foster conflict between the United States and another country, like Shia Iran, and by stirring US-Shia tension in Iraq.
Al-Qaeda has vowed to fight on and its new leader in Iraq, which it has named as Abu Hamza al-Muhajir, vowed in a web statement on Tuesday to avenge al-Zarqawi's death.
The name rang few bells and the US military said the new leader was probably al-Masri, who it says trained in Afghanistan and formed al-Qaeda's first cell in Baghdad.