(Associated Press file)
The hours-long attack differed from the Iraqi terror network's trademark car and truck bombings, a shift in tactics as the group struggles to regroup after being routed in a series of U.S.-Iraqi offensives.
Experts said the complex nature of the attack suggested the group's new leadership could be taking cues from the Taliban's success with similar operations in Afghanistan and Pakistan.
Al-Qaida in Iraq has been blamed for many of the deadly suicide strikes that have targeted the Foreign Ministry and other government institutions over the past year.
Sunday's violence differed because it involved bombings as well as an effort by suicide bombers to force their way into the building while battling with security forces. Such attacks were common during the sectarian violence that nearly pushed Iraq to the brink of civil war in 2006-2007, but they were usually blamed on Shiite militias or other groups.
Bruce Hoffman, a terrorism expert at Georgetown University, said it could be an attempt to evade the tightened security around government institutions following the ministry bombings earlier this year.
"It's not unusual for Iraq, but it is unusual for al-Qaida in Iraq," he said. "It could be that they were certainly influenced and motivated by the succession of attacks ... that have taken place in Kabul against government institutions."
The attack began with a series of bombs that tore through the commercial district near the central bank. Then insurgents trying to get into the building battled security forces for about three hours, bringing one of the busiest parts of the capital to a standstill as employees fled the area.
In all, as many as 26 people were killed and dozens wounded from the bombings and the shooting.
In a statement posted on a militant website, the Islamic State of Iraq, which includes al-Qaida, said five men armed with weapons and explosive belts were sent in what it called a "unique" attack against the financial institution.
"The bank was targeted because it is the artery that feeds the Satanic alliance with life via oil money and the stolen wealth of Muslims," the statement said, using common militant rhetoric for the United States and its allies.
Photos posted on the same website showed the disfigured heads and body parts of men dressed in army fatigues buried in the rubble of what al-Qaida said is the Central Bank.
Video surveillance footage from the Central Bank seen by an Associated Press reporter showed an armed man dressed in army fatigues storm in the bank's back door and exchange fire with security guards. He is shot in the leg and falls to the ground before his explosive vest detonates. Two other militants then flee the bank while shooting behind them, then set off their vests.
The assault has stoked fears that insurgents are taking advantage of political deadlock following March 7 elections to try to derail security gains as the U.S. prepares to withdraw its forces by the end of next year.
U.S. and Iraqi officials hailed the deaths of the top two al-Qaida in Iraq leaders -- Abu Ayyub al-Masri and Abu Omar al-Baghdadi -- in an operation in April as a major blow to the group. But a series of bombings that followed has illustrated the resilience of the group.
"Al-Qaida has been able to succeed in continuing to launch devastating strikes against the Iraqi government and creatively exploit loopholes left by Iraqi security forces," said Evan Kohlmann, of globalterroralert.com, a private, U.S.-based terrorism analysis group.
He said Sunday's attack appeared to be a show of force aimed at undermining confidence in the Iraqi forces.
"The longer the commandos can hold their ground against their numerically superior adversaries, the more they can extend the psychological and political impact of the operation," he said.
The persistent violence also has raised concerns about the readiness of Iraq's government to take over responsibility for security as the U.S. prepares to withdraw its forces by the end of next year.
Also on Thursday, an anti-al-Qaida fighter and four family members were killed as they slept in their garden to escape the heat in a former insurgent stronghold west of Baghdad, officials said. It was the second attack against Sunni figures who have turned against the terror network in as many days.
Gunmen broke into the house of Khudr al-Issawi and opened fire on him and his family during the pre-dawn attack in a village near Fallujah, 40 miles (65 kilometers) west of Baghdad. The farmer, his wife, two daughters and a son were killed, according to local police chief Brig. Gen. Mahmoud al-Issawi. Another son was wounded.
Associated Press Writers Qassim Abdul-Zahra, Hamid Ahmed and Hadeel al-Shalchi contributed to this report.