"After preliminary investigations, it was proven that the arrested Al Qaeda person is not Abu Omar al-Baghdadi, but, in fact, another important Al Qaeda official," said Brig. Gen. Qassim al-Mousawi, an Iraqi military spokesman. "Interrogations and investigations are still under way to get more information."
Al-Mousawi declined to give the suspect's name on Saturday.
Also Saturday, a suicide car bomb struck Baghdad's Shiite militia stronghold of Sadr City, killing at least 10 people, police said. The bomb hit an Iraqi patrol and scattered burning debris for hundreds yards, witnesses said.
It was al-Mousawi who announced late Friday that al-Baghdadi had been captured. A senior adviser to Prime Minister Nouri al-Maliki also had told The Associated Press that al-Baghdadi had been taken into custody. The adviser spoke on condition of anonymity because he was not authorized to release the information.
The reported arrest followed rumors this week that al-Baghdadi's brother had been arrested in a raid near Tikrit.
Almost nothing is known of al-Baghdadi, including his real name and what he looks like; his capture would be difficult for officials to verify.
The man captured Friday was found along with several other insurgents in a raid on the western outskirts of Baghdad, officials said.
Al-Mousawi said the suspect at first identified himself as al-Baghdadi, and that his identity was corroborated by another man captured with him.
Al-Baghdadi is believed to lead the shadowy Islamic State of Iraq, an Al Qaeda-inspired group that challenged the authority of Iraq's elected government. He has also signed militant messages posted online, as the leader of the Mujahedeen Shura Council — an umbrella group that includes Al Qaeda in Iraq.
U.S. officials in Baghdad said they were looking into the arrest but could not confirm the suspect's identity. In Washington, Defense Department spokesman Bryan Whitman said Pentagon officials had received no official confirmation that al-Baghdadi was captured.
U.S. and Iraqi forces have increasingly focused on al-Baghdadi's group in their fight against Sunni insurgents, especially the hardcore religious extremists who have shown no interest in negotiating an end to their struggle.
But some analysts have pointed out that the Al Qaeda-linked extremists rebounded following the death last June of Abu Musab al-Zarqawi, the charismatic Al Qaeda in Iraq leader who died in a U.S. airstrike in Diyala province.
The self-styled Islamic State of Iraq was proclaimed in October, when a militant network that includes al-Qaida in Iraq announced in a video that it had established an Islamic state in six provinces — including Baghdad — that have large Sunni populations, along with parts of two other central provinces that are predominantly Shiite.
Since then, the trappings of an Islamic shadow state with Al Qaeda as its base has been taking shape in some towns and cities of Anbar province where a government presence hardly exists, according to Sunni residents.
Residents of Sunni insurgent areas north and west of the capital have reported seeing handbills posted on walls in the group's name warning against un-Islamic behavior such as drinking alcohol.
Some residents of Anbar say Islamic State members have on occasion publicly flogged men for other offenses such as wearing long hair or harassing women and provided cooking fuel to residents in areas where the Iraqi government has little presence.
In its numerous Web postings, the Islamic State refers to punishment meted out by Islamic courts, although it is uncertain if these meet any standard under Islamic jurisprudence.
On Friday, the Islamic State of Iraq announced it would soon release a video on the death of a U.S. Air Force pilot whose F-16 jet crashed Nov. 27 north of Baghdad, according to IntelCenter, which monitors insurgent Web sites.
The pilot, Maj. Troy L. Gilbert, was listed officially as "whereabouts unknown" but then reported by the U.S. military as dead following DNA tests from remains at the scene. IntelCenter said it was unclear what the video would show.
The Islamic State has also claimed responsibility for downing several of the U.S. helicopters lost since Jan. 20, including one in Diyala province that killed 12 soldiers and a Sea Knight transport helicopter north of Fallujah that killed seven.
On Saturday, U.S. forces killed one suspected insurgent and captured 33 others in raids across Iraq, the military said.
Most of the operations, which took place late Friday and early Saturday, targeted Al Qaeda in Iraq and locals accused of providing support to the terror group, the military said in a statement.
Elsewhere, a roadside bomb killed three Iraqi policemen and wounded another in central Ramadi, 70 miles west of Baghdad, police said.
Gunmen opened fire Saturday on Shiite pilgrims in Latifiyah, about 20 miles south of Baghdad, police said. One person was killed and three were wounded.
The pilgrims were on their way back from a Shiite shrine in Karbala, where millions of faithful were performing rites this weekend for Arbaeen, a holiday that marks the end of a 40-day mourning period after the death anniversary of the Prophet Muhammad's grandson.
Some 340 people, mostly Shiite pilgrims en route to Karbala, were killed in sectarian attacks this past week.