Heavily reinforced American troops launched their most ambitious offensive in Baghdad since the invasion of Iraq four years ago when they began an operation at the weekend to seize back control of the lawless capital.

As the city came back to life after a four-day curfew, US commanders said that the “surge” reinforcements of about 30,000 additional troops were now in place alongside thousands of extra Iraqi soldiers and police.

The five extra US combat brigades were ordered to Iraq by President Bush this year in what is widely seen as the last chance for his Administration to salvage something from the disastrous aftermath of the invasion. Lieutenant-General Raymond Odierno, the commander of US military operations in Iraq, did not conceal the scale of the mission. He estimated that “40 per cent [of Baghdad] is really very safe on a routine basis”, but that 30 per cent was lacking control and a further 30 per cent experienced a “high level of violence”.

While American troops are much more visible on the streets of Baghdad, the sprawling city is now riddled with Shia Muslim militias, Sunni insurgents and al-Qaeda fighters. Al-Qaeda was blamed for last week’s bombing of the al-Askariya shrine in Samarra, a Shia holy site that was targeted in order to inflame sectarian violence between Islam’s two dominant sects.

General David Petraeus, the overall commander of US forces in Iraq, said that the US offensive would put American troops in the heart of al-Qaeda strongholds in Baghdad, many of them areas where US forces have rarely entered in the past.

The US military said yesterday that it had recorded some initial success with the killing of ten Iraqi militants and the arrest of a dozen more in a series of raids in the capital.

Violence against Iraqis continued, however. The body of Filaih Wadai Mijthad, the managing editor of al-Sabah daily newspaper, was found dumped in eastern Baghdad.

He had been shot several times and became the latest of nearly 200 journalists killed in Iraq over the past four years.

Military experts believe that the task of subduing Baghdad could take years to complete and that the US force is still probably too small to succeed.

The mission is also bound to increase the US military death toll, which currently stands at more than 3,520.

In spite of the odds, General Petraeus and his soldiers have only two months, during the blistering heat of the Iraqi summer, to produce results in time for his testimony before the US Congress in September.

If the military challenges are daunting, then the political obstacles in the way of reconciliation between Iraq’s various communities loom even larger. The American surge operation is intended to give Iraq’s political leaders the breathing space to agree a series of compromises that envisages an equitable distribution of the oil wealth, changes to the constitution and other goals to keep this fractured country in one piece.

Western officials, however, are deeply pessimistic about the chances of success.

Little or no progress has been made and a succession of senior US officials, led by Robert Gates, the visiting US Defence Secretary, has been building up pressure on Nouri al-Maliki, the Iraqi Prime Minister, to offer concessions to rival Sunni and Kurdish groups.

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