How U.S. Forces Found Iraq's Most-Wanted Man

But as he claimed leadership over insurgents in Iraq in 2003, his stature soared, growing to rival even that of Saudi-born al-Qaeda founder Osama bin Laden.

U.S. forces placed a $25 million bounty on Zarqawi's head, the same reward offered for bin Laden. Maliki told al-Arabiya television that "we will meet our promise" concerning the reward; a military spokesman said it was too soon to tell if it would be paid.

U.S. commanders and officials have consistently called Zarqawi's al-Qaeda in Iraq organization the top threat to the country's security and made eliminating Zarqawi a priority. U.S. Ambassador Zalmay Khalilzad called him "the godfather of sectarian killing and terrorism in Iraq."

Some outside analysts, however, have said U.S. officials have long overemphasized his role, which by their account further waned in recent months during a growing rift between Iraqi and foreign-born insurgents.

After Hussein was captured, there was widespread speculation that the insurgency would weaken, but it steadily escalated.

A statement purportedly from al-Qaeda in Iraq, posted Thursday on an Internet site used by insurgent groups, said, "What has befallen us today will not affect our determination." Underscoring the continuing power of the insurgents, bombers struck three times in the Iraqi capital Thursday, killing at least 25 people and wounding dozens more.

Beginning in the months after the U.S.-led invasion that toppled Hussein in April 2003, Zarqawi used semiautonomous cells across the country to batter U.S. and Iraqi security forces and to conduct hundreds of bombings, beheadings and other terrorist attacks on civilians.

Among the bloodiest attacks claimed by his group was the August 2003 bombing of the U.N. headquarters in Baghdad that killed 23 people, including the organization's chief envoy. Zarqawi was also blamed for a string of bombings on March 2, 2004, that killed more than 100 worshipers in Karbala and Baghdad during the Shiite festival of Ashura.

He is believed to have personally beheaded two American civilians abducted in 2004: Nicholas Berg, 26, an entrepreneur from West Chester, Pa., and Eugene "Jack" Armstrong, a 52-year-old contractor from Hillsdale, Mich. A video showing Berg's decapitation was posted on the Internet, one of the first in a string of such postings that year.

Earlier this year, al-Qaeda in Iraq recast itself as part of a coalition of insurgent groups called the Mujaheddin Shura Council. That move corresponded with a shift toward a more intense focus on attacks against civilians, most of them Shiites, and calls for civil war between Sunni Arabs and Shiites.

Sectarian violence has increased markedly nationwide since the bombing in February of a Shiite shrine in Samarra, north of Baghdad. The Iraqi government pinned the attack on Zarqawi, though al-Qaeda in Iraq denied involvement.

In an audiotape released last week, Zarqawi called on Iraqi Sunnis to kill Shiites, including Grand Ayatollah Ali Sistani, the country's most revered Shiite cleric.