U.S. military planners have assembled a special task force charged with finding and neutralizing Jordanian terror leader Abu Musab al-Zarqawi (search), U.S. officials told FOX News.

Known as Task Force 626, the operation is assembled along the same lines as that of Task Force 121 (search), which searched months before capturing Saddam Hussein and is still hunting Usama bin Laden.

Task Force 626 is smaller than its higher-profile sibling but is similarly made up of CIA operatives, special operations troops from the Navy and the Army, and a handful of investigators.

Members of 626 have fanned out in areas ranging from Baghdad to Fallujah and other areas in the contested al Anbar province in search of al-Zarqawi. While al-Zarqawi is still at large, officials say the task force and other military units have been very successful in eliminating many leaders of his group's leadership.

Many key al-Zarqawi figures have been "whacked," one official told FOX News, citing the missile strike that took out al-Zarqawi's spiritual guide and advisor late last week.

Officials believe they may have taken out as much as half of the members of the senior leadership of al-Zarqawi's group, Tawhid and Jihad (search) — whose name is loosely translated as "Monotheism and Holy War," but they caution that the group harbors many more figures who could rise up and take their places.

Tawhid and Jihad this week claimed responsibility for kidnapping and killing two Americans — Jack Hensley (search) and Eugene Armstrong (search). The group is still holding Briton Kenneth Bigley (search).

The group demanded the release of all Iraqi women from Iraqi prisons but U.S. and Iraqi officials said they would not meet the group's demands although Iraqi officials expressed willingness to consider letting female prisoners out of prison.

Al-Zarqawi, standing alongside four other masked militants clad in black, personally cut off Armstrong's head, the CIA confirmed after analyzing his voice on a video that aired on a Web site Monday.

Armstrong's body was discovered only blocks from where he lived, officials and witnesses said.

Tawhid and Jihad has claimed responsibility for killing at least seven hostages, including another American, Nicholas Berg (search), who was abducted in April. The group has also said it is behind a number of bombings and gun attacks.

A host of militant groups have used kidnappings and bombings as their signature weapons in a blood-soaked campaign to undermine interim Prime Minister Ayad Allawi's (search) government and force the United States and its allies out of Iraq. The violence has already persuaded companies to leave Iraq, hindered foreign investment, led firms to drop out of aid projects, restricted activities to relatively safe areas and forced major expenditures on security.

President Bush defended his decision to invade Iraq and told a subdued U.N. General Assembly session Tuesday that the war, which was launched without U.N. approval, delivered the Iraqi people from "an outlawed dictator."

On the sidelines of the meetings, Bush told Allawi, "We will not allow these thugs and terrorists to decide your fate and to decide our fate. "

Allawi said: "The barbaric action of yesterday is really unbelievable."

In Monday's video, al-Zarqawi announced that Tawhid and Jihad was taking revenge for female Iraqi prisoners being held at U.S.-controlled prisons Abu Ghraib (search) and Umm Qasr and called Bush "a dog."

The U.S. military said women are not held at either facility but has acknowledged it is holding two female "security prisoners" elsewhere. They are Dr. Rihab Rashid Taha (search), a scientist who became known as "Dr. Germ" for helping Iraq make weapons out of anthrax, and Huda Salih Mahdi Ammash (search), a biotech researcher known as "Mrs. Anthrax."

More than 130 foreigners have been kidnapped in Iraq, and at least 27 of them have been killed. Many more Iraqis have also been seized in the chaos since Saddam was ousted last year, in many cases for ransom.

FOX News' Bret Baier and Ian McCaleb and The Associated Press contributed to this report.