Even as he announced that Zarqawi had been "terminated," Iraqi Prime Minister Nuri al-Maliki implicitly acknowledged that others would try to take his place, pledging: "Every time a Zarqawi appears, we will kill him."

Some security analysts played down the impact of his death, saying Zarqawi's network represented only a fraction of the wider insurgency in which less extreme resistance groups had gained in strength.

It was business as usual in Iraq on Thursday, with two bombs killing 15 people and injuring 36 in Baghdad within a couple of hours of Maliki's announcement.

"Other Zarqawis will soon spring up," said Nadim Shehadi of London's Chatham House think-tank. "The Iraqi insurgency is a very loose organization and I don't see how the decapitation of it will have such a great impact."

On the other hand, there is no known successor primed to take Zarqawi's place, and certainly no one with the universal recognition enjoyed by the man with a $25 million U.S. bounty on his head.

Zarqawi carefully plotted his ascent to the status of al Qaeda's top operational figure worldwide, swearing allegiance to bin Laden in 2004 and renaming his Tawhid wal Jihad (One God and Holy War) movement as the Iraqi arm of al Qaeda.

The United States fanned speculation of a rift last year when it released an intercepted letter in which bin Laden's deputy, Ayman al-Zawahri, criticised some tactics of the Iraqi insurgency including beheading of hostages and attacks on Shia civilians. He also questioned whether Zarqawi, a Jordanian, should cede leadership to a local.

Possibly in response to this, Zarqawi halted public beheadings and placed his group under the umbrella of a Mujahideen Council led by an Iraqi.

But the future of his strategy of "war against Shi'ites in all of Iraq" is one of the main questions raised by his death.

"It will be interesting to see whether someone will step in and carry on this divisive strategy of pursuing Sunni-Shia infighting," Ranstorp said.

"Will there be others who carry on this line, or is this the end of it? If it is the end of it, that's good news."