Making his first visit since the deployment of 30,000 additional US troops to Iraq last year, Mr Cheney characterised the changes in Iraq's security and political landscape as 'phenomenal' and 'remarkable'.

He said: 'If you reflect back on those five years, it's been a difficult, challenging, but nonetheless successful endeavour.'

'We've come a long way in five years,' he said at a news conference with Ambassador Ryan Crocker and Army General David Petraeus, the top US commander in Iraq.

His visit on Monday, as part of a 10-day tour of the Middle East, came on the same day that two US soldiers were killed by a bomb near Baghdad and a female suicide bomber killed at least 40 people outside a holy Shi'ite shrine in Karbala.

Mr Cheney, 67, took a trip outside the heavily fortified Green Zone during the day, through streets lined with troops, barricades and checkpoints.

Later, as he slept at Balad air base, 72km north-west of Baghdad, mortar fire could be heard throughout the night as US soldiers shelled suspected insurgent hideouts.

The five-year anniversary of the start of the war today has prompted a variety of appraisals. Not all of them are as upbeat as Mr Cheney's.

According to a new poll by ABC News and other news organisations, many Iraqis feel more optimistic because of a recent decline in violence, but they remain dissatisfied with the provision of basic services and job opportunities.

A 15-page report issued on Monday by the International Committee of the Red Cross concluded that a humanitarian crisis had left millions of Iraqis with inadequate clean water, sanitation and health care.

'Five years after the outbreak of the war in Iraq, the humanitarian situation in most of the country remains among the most critical in the world,' the report said.

Poor maintenance, insufficient fuel supplies, acts of sabotage and failure to conduct repairs threaten the electrical supply throughout Iraq, and many Iraqis rely on unsafe water sources, the report said.

The health-care system is in crisis because of shortages of supplies and hospital beds, as well as a shrinking pool of Iraqi doctors.

About 2,200 doctors and nurses had been killed and more than 250 kidnapped since 2003, the report said. It added that 20,000 of the 34,000 doctors registered in Iraq in 1990 had left the country.

'The Iraqi health-care system is now in worse shape than ever,' the report concluded.

'Many lives have been lost because prompt and appropriate medical care is not available.'

Although violence has subsided compared with a year ago - mostly due to the additional troop surge last year - Iraq remains a dangerous place.

On Monday, two US soldiers - there are 160,000 still stationed in the country - were killed when a bomb exploded on their vehicle north of Baghdad during a mission to clear a road of such explosives.

The attack raised the number of US soldiers who have died in Iraq to at least 3,990.

Another 29,395 have been wounded, according to Department of Defence figures.

WASHINGTON POST, AGENCE FRANCE-PRESSE, ASSOCIATED PRESS