June 8 (Reuters) – Jordanian militant Abu Musab al-Zarqawi,

al Qaeda leader in Iraq, was killed in an air strike on

Wednesday night. His death, announced on Thursday, raises

questions over the future of Iraq's Sunni Arab insurgency.

Major General William Caldwell, the chief U.S. military

spokesman, said an Egyptian militant trained in Afghanistan

named Abu al-Masari, who established the first al Qaeda cell in

Baghdad, may succeed Zarqawi as head of the group in Iraq.

Here are facts on some of the leading Sunni Arab insurgent

elements in Iraq seeking to topple the U.S.-backed, Shi'ite-led

government and expel American troops.

SADDAM HUSSEIN LOYALISTS

Former officers in ousted Iraqi leader Saddam Hussein's

regime are leading the Sunni insurgency. Their experience with

intelligence gathering make Saddam loyalists a deadly force.

There have been some unsubstantiated reports that they formed an

alliance with al Qaeda, providing logistics and funding.

AL QAEDA

Al Qaeda militants from across the Arab world make up only

about five percent of the Sunni Arab insurgency but their

spectacular suicide bombings kill the most people. It's not

clear if Zarqawi's death will provide more inspiration or weaken

the movement. Al Qaeda fighters are said to have alienated Sunni

tribal leaders with their brutal methods of killing.

MUJAHIDEEN SHURA COUNCIL

An umbrella body composed of al Qaeda in Iraq and some other

militant groups to coordinate their fight against U.S.-led

forces and the Iraqi government. It is made up of al Qaeda, the

Army of the Victorious Sect and four lesser known Sunni groups.

Its aim is to confront the "Crusaders and their rejectionist

(Shi'ite) and secularist followers who have seized Baghdad".

ANSAR AL-ISLAM

Ansar al Islam (Supporters of Islam) is made up mostly of

Kurds who follow an extremist brand of Islam and has close links

with al Qaeda. The group is blamed for a number of attacks,

including assassination attempts against Kurdish officials.

IRAQI NATIONAL ISLAMIC RESISTANCE 1920 REVOLUTION BRIGADES

This group, whose name refers to Iraq's history of fighting

British colonialism, apparently wants to liberate Iraq from

occupation and establish a new Islamic state. It has claimed

responsibility for attacks on U.S. troops, including the downing

of two helicopters in 2004.

IRAQI RESISTANCE BRIGADES

Iraqi Resistance Brigades has claimed responsibility for

several attacks against U.S. troops. The group has distanced

itself from others linked to Saddam Hussein loyalists.

JAYSH MUHAMMAD (THE ARMY OF MUHAMMAD)

The group appears to be mainly Saddam Hussein loyalists from

his former intelligence, security and police forces who took on

an Islamic militant identity.

THE MISSION OF ARMED VANGUARDS OF MUHAMMAD'S SECOND ARMY

This organisation is waging Jihad to evict U.S. forces from

Iraq and has threatened to attack any Muslim that cooperates

with the United States in Iraq. It was one of several groups

that claimed responsibility for the 2003 bombing of the United

Nations headquarters in Baghdad.

(Writing by Michael Georgy, edited by Dominic Evans)

REUTERS