Maliki Aide Who Discussed Amnesty Leaves Job

Roadside bombs -- known as improvised explosive devices, or IEDs -- accounted for more than half of the deaths this year. Hostile fire from small arms and other weapons were the second-biggest cause of death. To date, 528 of the deaths have been non-hostile, resulting from accidents, illness, suicides and other causes.

"What is significant and troublesome is that the casualty rate per month hasn't really declined," said Michael O'Hanlon, a military analyst at the Brookings Institution here. "Unfortunately, any hopes we had that we have come to the end of this rate of taking casualties have been dashed."

At this rate, if the war extends until 2008, "it's very likely that victory will mean 4,000 killed," said Anthony Cordesman, a military historian at the Center for Strategic and International Studies.

The number of Iraqi civilians and military personnel killed since the start of the war ranges from 43,000 to 49,000, according to estimates from news agencies, research groups and other sources.

The issue of Zarqawi's successor has been a major question for Iraqi and U.S. officials. In the days following Zarqawi's death, several presumed candidates surfaced in statements appearing on Web sites used by militant groups. One statement, in the name of al-Qaeda in Iraq, was signed by Abu Hamza al-Muhajer and vowed to avenge Zarqawi's death.

At a news conference Thursday in Baghdad, a U.S. military spokesman said Muhajer had been identified as Masri. "We think they are one and the same at this point," said Maj. Gen. William B. Caldwell IV. "We'll continue to do further analysis."

"Al-Masri's intimate knowledge of al-Qaeda in Iraq and his close relationship with [Zarqawi's] operations will undoubtedly help facilitate and enable them to regain some momentum if, in fact, he is the one that assumes the leadership role," Caldwell said.

Beyond some bare facts, little is certain about the person whose photograph -- showing a youthful man with neatly trimmed facial hair, in traditional white Gulf Arab dress -- was released in Baghdad by the U.S. Central Command. Officials in Washington said Masri is also known -- and equally unknown -- by the name Yusif al-Dardiri.

The question of who takes over Zarqawi's leadership role is important, one counterterrorism official said, because of perceived past divisions between al-Qaeda and Zarqawi's operations in Iraq. Last October, the U.S. government released a letter it said had been intercepted en route from Zawahiri to Zarqawi expressing concerns about public beheadings of hostages in Iraq and attempts to foment divisions between Sunnis and the majority Shiites.

"Zawahiri's big issue was the negative publicity that those attacks were generating," said the official, who said he was not authorized to discuss the subject on the record. The question now, he said, was whether Masri's primary allegiance is to his Egyptian mentor, Zawahiri, or to Zarqawi.

U.S. analysts have also been watching carefully for signs of a split between domestic-led Sunni groups with nationalistic aims in Iraq and those elements of the insurgency whose goals are more in keeping with bin Laden's overall objective of expanding violent jihad across the Arab word.

Staff writers Karen DeYoung and Ann Scott Tyson in Washington contributed to this report.