The Iraqi Government today launched its biggest military offensive yet against the insurgency, capitalising on a power vacuum created by the wounding of its commander Abu Musab al-Zarqawi.

More than 40,000 Iraqi soldiers will take part in Operation Thunder, aimed at turning the tide against anti-Government guerrillas who have killed more 620 in the past month.

Another 15 people - including a child, a university lecturer and three police officers - were killed today in bombings and drive-by shootings.

Supervised by the US, the Iraqi troops will set up a cordon around militant strongholds in Baghdad and carry out operations to capture the remaining insurgents.

Conflicting internet reports suggest confusion among the higher echelons of al-Qaeda In Iraq, which is struggling to retain co-ordination of its activities following the serious injury to al-Zarqawi.

A message on one Islamist website said that Abu Hafs al-Qarni, a little-known Saudi deputy to al-Zarqawi, had been appointed as his temporary successor. But shortly afterwards the claim was retracted and denounced.

Both announcements were signed by the information section of al-Zarqawi's group, the Al-Qaeda Organisation in the Land of Two Rivers. The retraction was made in the name of Abu Maisara al-Iraqi, a regular contributor who first signalled that al-Zarqawi had been hurt.

Bayan Jabr, the Iraqi Interior Minister, today confirmed that he had received intelligence confirming rumours that al-Zarqawi - who carries a $25 million US bounty - was seriously wounded in a gun battle on Saturday.

He said: "We are not sure whether he is dead or not, but we are sure that he is injured."

Saadoun al-Duleimi, the Defence Minister in the newly appointed coalition cabinet, said that the renewed operation would shift the government firmly on to the offensive.

"We shall not leave any place for terrorists or those who shelter them and incite terrorism in Iraq," he said. "We will stand against all those who try to shed Iraqi blood. We will implement the law with everything we’ve got."

He added: "By next week we will have a strong and safe cordon around Baghdad like a bracelet that surrounds the hand. We will not allow anyone to cross this cordon."

Mr Jabr said that 675 checkpoints plus an unspecified number of mobile checkpoints would be created, dividing the capital into two distinct sectors. Each would be subject to high-profile patrols.

If the confusion in cyberspace suggests the leadership is in turmoil, the insurgency on the ground continued apace today. A car bomb exploded in northern Baghdad near a police patrol, killing five people, including three police officers, and wounding 17.

Gunmen shot dead Iraqi army Captain Awas Youssif Hassan in Khalis, 35 miles north-east of Baghdad. A child was killed during clashes between US forces and insurgents in northern city of Tal Afar, 93 miles east of the Syrian border.

And gunmen in a speeding car fired automatic weapons at commuters in Baghdad’s southern Risala district, killing four Iraqis, including a university professor and a translator working for the US.

Richard Beeston, Diplomatic Editor of The Times, who is in Baghdad, said: "There was a report on the internet yesterday that four lieutenants were potentially in place to succeed Mr al-Zarqawi, but we are dealing with very shaky information sources.

"Al-Qaeda remains a very shadowy organisation and there is a high level of confusing disinformation being put out. The areas in which the insurgency is based in Baghdad are no-go areas for journalists and many others, so it's extremely difficult to verify anything at present. We will have to wait until a video or some form of official announcement is made."

Donald Rumsfeld, the US Defence Secretary, warned that a long line of potential insurgent leaders was waiting in the wings to succeed Mr al-Zarqawi. He told a foreign affairs group in Philadelphia: "Despite the successes, new terrorist leaders continue to step forward, and new networks emerge."

Al-Zarqawi, a Jordanian, is blamed for some of the bloodiest assaults in Iraq. He has claimed scores of suicide bomb attacks against civilians and the security forces, executions of government officials, and the kidnapping and beheading of foreigners, including Ken Bigley and Margaret Hassan.

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