THREE months ago Abu Musab al-Zarqawi was said to be badly injured and close to death. But in the space of two days the world’s most active terrorist has demonstrated in typically bloody fashion that he is back at the head of Iraq’s most ruthless and powerful insurgent group.

With yet more suicide bombings in Baghdad yesterday, killing 29 people, there were fears that the city was about to suffer a fresh wave of terrorism intended to exacerbate sectarian conflict between Shia and Sunni Muslims and destroying the new constitution that was supposed to bring the various ethnic and religious communities together.

President Talabani of Iraq, addressing the UN summit in New York, begged world leaders for help. “Today Iraq is facing one of the most brutal campaigns of terror at the hands of the forces of darkness,” he declared.

In Baghdad Sadoun al-Dulaimi, the Iraqi Defence Minister, called al-Zarqawi’s latest violence the act of a madman. “We will neither forgive them, nor allow them to retain an inch of Iraq,” he said after the latest bombings, whose victims included 15 elite police commandos blown up in their truck.

Mr al-Dulaimi called the insurgents “morally bankrupt” and insisted that their cause was on its “last legs”, but unfortunately for Iraq his assessment is probably more wishful thinking. Al-Zarqawi’s tactics, which include the mass murder of Shia civilians, beheading Western hostages and assassinating government officials, are certainly brutal. But there is a method to his madness.

He is responsible for making large areas of central Iraq ungovernable. His insurgent campaign has successfully challenged the might of the US military. He has persuaded his militant followers that it is possible to stop a democratic Shia-led government ruling Iraq and to replace it by a Sunni Islamic caliphate in Baghdad that would resemble Afghanistan under the Taleban.

In a recording broadcast on an Islamic website on Wednesday, he delivered a chilling message to his adopted country. “Al-Qaeda Organisation in Iraq . . . has declared war against Shia in all of Iraq,” he said. Then, addressing himself to the Shia-dominated Government, he declared that it had provoked a new battle against his forces in Tal Afar, a northern town.

Al-Zarqawi’s threats carry more weight than ever. Only two years ago his group was a fringe organisation that attracted a handful of fanatic Islamic militants.

Today it is the richest, best organised, best armed and most powerful insurgent force in Iraq, with thousands of volunteers, including some from around the Middle East and beyond, prepared to fight and die for their cause. His slick propaganda department can record a suicide attack, release it within an hour on the internet and relay it into the homes of Muslim sympathisers around the world.

In the immediate future, senior US military sources are sure that al-Zarqawi will lead a lethal campaign to disrupt Iraq’s referendum on its new constitution scheduled for next month and continue the campaign against future elections, which he has branded a “heresy” against Islam.

The news is bad enough for Iraq, but experts fear that al-Zarqawi intends to spread his campaign across the Middle East, into Europe and even into America.

Jean-Charles Brisard, the author of Zarqawi: The New Face of al-Qaeda, said that last month’s failed rocket attacks by al-Zarqawi’s fighters against US warships docked off the Jordanian coast at Aqaba should serve as a warning to the region. “I believe that his fight will not stop in Iraq. There is intelligence that his people were travelling in Europe a few weeks ago.”

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