AMERICAN armoured divisions seized parts of Saddam International Airport last night, leaving roads littered with deserting Iraqi soldiers’ combat boots and uniforms in their wake.

The entire city of 5 million was plunged into darkness after loud explosions thundered through the capital. Iraqi soldiers started to set up road blocks across the city for the first time since the war began two weeks ago.

Eyewitnesses reported fighting and loud explosions on the southwestern edge of Baghdad, near the airport, some 12 miles from the ruins of the government district in the centre.

The battle for the airport began shortly after Baghdad’s city-wide power failure. Small units of British and American forces sought to capitalise on the blackout by swooping on key centres of Saddam Hussein’s rule.

Early this morning a flurry of at least 16 loud explosions in the capital sent huge plumes of smoke into the sky as aircraft roared overhead. Pentagon chiefs said that Central Command had not targeted Baghdad’s electrical grid, but the coalition sought to exploit the power loss with a series of forays to assess defences, scout Baath Party buildings and check centres of the feared Special Security Organisation.

The missions, led by the SAS and the US Delta Force and Navy Seals, also aimed to check the mood on the streets.

The action came as President Bush exposed sharp differences with Britain by declaring US forces to be within sight of victory. Mr Bush told wildly enthusiastic Marines at Camp Lejeune, North Carolina: “Having travelled hundreds of miles we will now go the last 200 yards. The vice is closing and the days of a brutal regime are coming to an end.”

Although he conceded that there was “work ahead”, Mr Bush’s optimism contrasted with a much more sober assessment in London. Geoff Hoon, the Defence Secretary, had earlier cautioned against viewing the rapid advance on Baghdad as the beginning of the end of the military campaign.

“Do not underestimate the task that still faces our forces or the length of time it may take to complete. We are still very much in the second phase of steady progress,” he said.

Donald Rumsfeld, the US Defence Secretary, said that American forces were “closer to central Baghdad than many American commuters are from their downtown offices”. As he spoke US armoured columns swept almost unimpeded to within five miles of the Iraqi capital.

Several hours later American forces were in control of at least part of the airport. Securing it would open the door for the US to fly military support and humanitarian aid to the heart of Iraq.

Some American advanced units doubled back, heading south to clear any Republican Guard forces outflanked by the advance. US military officials said that up to four Republican Guard divisions were moving south from Baghdad to defend the capital.

Mr Bush indicated that US forces would push on. “The course is set. We are on the advance. Our destination: Baghdad. We will accept nothing less than complete and final surrender,” he told the Marines.

Shortly after he spoke the lights went out in the Iraqi capital for the first time since the war began 15 days ago. The power failure followed 15 minutes of intense aerial bombardment, and led to suggestions that the US had dropped its “blackout” bomb, which uses thousands of carbon-fibre filaments to short-circuit electrical grids.

General Richard Meyers, Chairman of the Joint Chiefs of Staff, said: “Central Command has not targeted the power grid in Baghdad.”

His denial left open the possibility that covert teams from the Central Intelligence Agency may have been responsible. The Pentagon was criticised after hospitals were left without power when it dropped two blackout bombs in the Kosovo campaign. Earlier, US special forces raided one of Saddam’s presidential compounds 56 miles north of Baghdad. The force returned empty-handed, but the raid appeared to be designed to unsettle Iraq’s leaders, showing that US forces were moving around the country at will.

Coalition forces received a boost when the leader of Iraq’s Shia Muslims told his followers to not to hinder coalition forces. Grand Ayatollah Ali al-Sistani, who has been under house arrest on Saddam’s orders, issued the edict from the holy city of Najaf. In London the Shia Al Khoei foundation confirmed the ruling. It said that until now the ayatollah’s followers had been confused over whether to fight the American forces.

US military chiefs greeted the news as a breakthrough in the “hearts and minds” war. Tension in Najaf, however, remained high. A US convoy was forced to retreat by a crowd that believed it was heading for the venerated shrine of Imam Ali.

Coalition chiefs were buoyed but bemused by the advance over the past 48 hours, in which not a single American soldier was lost to enemy fire during the comprehensive rout of two Republican Guard divisions defending Baghdad.

“This was painted by the Iraqi regime as the big fight.” one officer said.

“We would expect there to be more troops between where we are and the heart of the city. Where was the potent fighting force?” Some of the famed Medina Division could have fallen back to Baghdad before the US 3rd Division advanced north of Karbala, he said. US control of Highway 6 from Kut to the capital meant, however, that there was no easy escape for the Baghdad division.

British commanders, whose responsibility is for southern Iraq, heaped praise on the US advance. Air Marshal Brian Burridge reportedly told senior officers: “That is one of the most impressive pieces of manoeuvre warfare that there has ever been and people will by writing about this in staff colleges for decades.”

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