A previously unknown militant will succeed terror leader Abu Musab al-Zarqawi, al Qaeda in Iraq announced Monday.

In a web statement posted just days after Zarqawi was killed in a U.S. air raid, al Qaeda named Abu Hamza al-Muhajer as "successor in the leadership of the organization."

The statement, which could not be independently verified, said Muhajer was "a beloved brother with jihadi experience and a strong footing in knowledge."

The announcement came as U.S. military officials revealed that Zarqawi died of internal injuries caused by Wednesday's bomb blast.

Col. Steve Jones, command surgeon for Multinational Forces, told a news conference that the al Qaeda in Iraq leader was declared dead 52 minutes after the first U.S. air strike against his safe house.

An autopsy revealed he died from serious injuries to his lungs.

"Blast waves from the two bombs caused tearing, bruising of the lungs and bleeding," Jones said.

"There was no evidence of firearm injuries."

Jones said Zarqawi's spiritual adviser, Sheik Abdul-Rahman, was killed instantly in the strike.

DNA tests positive

The FBI confirmed Monday that DNA evidence positively identified the body as that of Zarqawi.

The Jordanian-born terror leader, who was said to be responsible for numerous beheadings of foreign and Iraqi hostages, was killed after two 225-kilogram bombs were dropped by U.S. jets on Wednesday evening.

He was killed along with seven aides in a safe house 50 kilometres northeast of Baghdad in the volatile province of Diyala.

Maj. Gen. William Caldwell, a spokesman for the U.S. military in Baghdad, said U.S. forces arrived about 28 minutes after a fighter jet bombed Zarqawi's hideout outside Baqouba.

Medics secured Zarqawi's airway but his breathing was shallow and labored, and he expelled blood from his mouth.

"It was very evident he had extremely massive internal injuries," Caldwell said.

Meanwhile, the top American commander in Iraq rejected as "baloney" an account by an Iraqi eyewitness who said a dying man resembling Zarqawi had been beaten by American troops after the airstrike.

"Our soldiers who came on the scene found him being put in an ambulance by Iraqi police. They took him off, rendered first aid, and he expired," Gen. George Casey Jr. told Fox News on Sunday.

Security crackdown

Meanwhile, nine people, including two children, were killed Monday as U.S. forces raided a house close to where Zarqawi died in last week's air strike, military commanders said.

The seven adults were described as insurgents linked to al Qaeda in Iraq and were killed in what appeared to be a follow-up to the attack that killed Zarqawi.

A U.S. military statement said troops were fired on by insurgents using a machine gun from a rooftop, after which U.S. planes "immediately suppressed the enemy fire, killing seven".

The attack took place shortly after Iraqi and American officials revealed they were planning a new security crackdown in Iraq after al Qaeda vowed to carry out "major attacks'' following Zarqawi's death.

A web statement last week said the group had renewed its allegiance to al Qaeda leader Osama bin Laden.

Bin Laden "will see things that will bring joy to his heart,'' said the statement. 

The group vowed "to prepare major attacks that will shake the enemy like an earthquake and rattle them out of sleep.''

Iraq's new Sunni Arab defence minister says a security plan will be put in place around Baghdad to deal with a possible surge in terror attacks.