KABUL (CP) - Riots that killed more than 20 people and destroyed dozens of buildings, including international aid offices, was not a backlash against western countries that are helping to rebuild Afghanistan, a senior UN official said Monday.

Last week's rioting, which included the looting and burning of Afghan businesses, was simply the work of criminals who inflamed a crowd of people angry about an accident involving a U.S. military truck, according to Tom Koenigs, special representative of the UN secretary general.

While damage to buildings is being repaired, the damage to Afghanistan's image will hamper business investment needed to improve the standard of living of the country's poor, he said.

"These riots are poison for the economic development of Kabul," Koenigs said Monday at a new conference.

"It will frighten investors. Anti-foreigner resentments will make the donor nations wonder whether they are really liked or not."

Koenigs said the United Nations will not be scared off by such incidents.

Economic recovery may be slow, but most Afghans are enjoying a better standard of living and safer communities than they have in years. People want to get on with improving their lives, he said.

"Even after last Monday I have no reason to doubt the explicit and strong will of the vast majority Afghans to peace," Koenigs said.

The May 29 crash, which U.S. officials suggest may have been caused by brake failure, is believed to have killed five Afghans directly. As many as 20 others died in the subsequent rioting.

Since then things have mostly returned to normal. Curfews have been lifted. Outside a blackened burned-out building destroyed in the riot, two children sit on the sidewalk playing with toys as their father calmly repairs a bicycle.

People glide past scores of tiny shops and fruit stands all open for business. Phone card vendors bravely hop through insane traffic to hawk their wares.

The passing crowd breaks around a shoal of three police officers, automatic rifles resting on their laps, as they sit and doze in the hot afternoon sun, seemingly oblivious to noisy and colourful scene around them.

Abdul Qahar, 50, who earns a living cooking at marriage banquets, said life is hard but it is slowly getting better.

Food prices are too high, but he feels much safer then when the Taliban were in power.

He said the government would be more popular if it started lending some the billions of dollars in foreign aide money to poor people to start or expand their businesses. Maybe someday, he said with a smile.

"Not all Afghans are involved in these riots," Qahar said from a hill overlooking his neighbourhood.

"I'm happy. Something is better than nothing. Please be optimistic about Afghanistan."

There are two separate investigations into the accident that sparked the riot, one by the U.S. army and another by the Afghan government.

Meanwhile, some foreign business owners involved in reconstruction projects in Afghanistan are considering beefing up security in the wake of the melee.

Robert Carver, president of Natless, a construction and logistics support company, has lived in Kabul for six years.

He acknowledged there is growing tension in the religious community about poverty, prostitution and the growing number of bars in Kabul.

Part of him shrugs off the riot but another part wonders what is really going on in a city of three million that is swelling with a growing number of desperately poor refugees from the countryside.

"Things have calmed downed but it is probably going to get worse," said Carver, who is from Oklahoma. "It could happen again. There must be an underlying frustration that I don't even know."

An official with an international aid agency was taking the violent outbreak in stride, even though the mob stopped only a few metres from the agency's office. No new security provisions. No changes to procedure. There is just too much work to do.

"We don't feel too concerned about this," said the official who declined to be named. "People are used to it. You can't repair the effects of 20 years of war in six months. It takes time."