Within days of taking over as chief administrator on May 30, Paul Bremer had dismantled the army, police and other security forces and banned 30,000 senior members of Mr Hussein's ruling Ba'ath party from holding government positions. Overnight, law and order collapsed and borders with neighbouring countries became porous, the experts said.

US-based Iraq researcher Ahmed Hashim said that with American-led forces unable to adequately fill the vacant security and policing roles, groups opposing the occupation were free to flourish. Their activities were being boosted by dissidents crossing unchecked from Saudi Arabia, Syria, Turkey, Jordan and Iran.

'They range from Southeast Asian to Arab Afghans to Chechens to the more extremist groups who want to fight the US presence in Iraq,' said Dr Hashim, a professor at the Centre for Naval Warfare Studies in Newport, Rhode Island. 'The situation is so chaotic that the attacks against foreigners could be the work of a number of groups.'

Expressing his own opinion rather than that of the government institution he works for, he said the foreign infiltrators were joining forces with Iraqi groups as they would be unable to work alone. This was damaging the coalition's efforts to rebuild Iraq.

'More force is going to be dedicated to protecting people, rather than engaging in reconstruction or restoring law and order,' he said. Analysts believe the UN was not targeted as an organisation, but because it was part of the coalition rebuilding Iraq. They would not speculate on which group was responsible.

Disrupting the occupation in the name of Iraqi sovereignty was the aim of the spate of worsening attacks, the analysts agreed. Al-Qaeda's influence could be seen, while remnants of Mr Hussein's regime were actively agitating.

Robert Rabil, project manager with the Iraq Foundation in Washington, believed bonds had been formed between Muslim extremists and others loosely affiliated to al-Qaeda and Iraqis opposed to the American-led coalition.

'They have a mutual, common enemy and are co-operating with each other,' said Dr Rabil, who worked with the Red Cross during the war in Lebanon. He feared Iraq would become a magnet for Islamic militants seeking to wage a holy war against the foreign forces.

'We faced the same things in Lebanon,' he said. 'Car bombs and the like we knew were most likely planned from the outside but co-ordinated and brought into action from the inside. To prevent Iraq from becoming another Lebanon, Iraqis have to work with the coalition forces.'

Lebanon was devastated by a civil war from 1975 to 1990.

American Middle East specialist Phebe Marr said reconstruction efforts would be severely disrupted because it would be difficult to convince companies and aid workers to go to Iraq.

But she wondered whether the efforts to destabilise would backfire.

'This was an attack on the international community because innocent people were killed,' said Dr Marr, a retired senior fellow at the National Defence University and author of Modern History of Iraq.

'It's going to jolt Iraqis because it can't be read as an attack on the occupation.'

Iraqis had a right to be angry that the US had not put enough forethought into the basic facets of a post-Saddam Iraq - electricity, water and security. The necessary resources had not been put into the reconstruction plans.

'The bulk of the Iraqi people understand that the US and the international community have to stay until Iraq has been put back together,' Dr Marr said. 'The people who are bombing and want the US to leave really don't have mass support. It would be a disaster for most people if the US pulled out now.'