On the streets of Baghdad, people covered their mouths with masks, scarves and other bits of clothing as sand whipped across the city. Doctors said the weather was aggravating respiratory conditions, especially among the elderly.

'We received 35 emergency cases since the early morning,' said Dr. Nihad Jabar, who works in the emergency wing of Baghdad's Ibn al-Nafis Hospital.

He said most were treated and released but that four people over 60 were admitted to intensive care 'because their cases are very critical.'

Dr. Moayid Ala, at the same hospital, said the number of people suffering from respiratory problems is increasing each year. At the crosstown Kindi hospital, officials said they admitted 17 people, most with asthma-related difficulties.

Sandstorms are a regular occurrence in Baghdad, which is shielded from the desert by a thin strip of arable land between the Tigris and Euphrates rivers.

But many Iraqis believe there has been a spike in dust storms in recent years, even if there is no scientific evidence to back this up.

In Apr, one of the worst storms in years left a thick layer of yellow dust on houses and cars in Baghdad, forcing the closure of the city's international airport and hampering military flights.

On that occasion, militants from eastern Baghdad seemed to take advantage of the reduced aerial activity, repeatedly shelling the Green Zone.

The US military had no knowledge of any such attacks on the area in Baghdad's center on Thursday, according to Tech. Sgt. Chris Stagner, a military spokesman.

One man told AP Television News on Thursday that he struggles to breathe whenever a serious sandstorm occurs.

'So I go to the hospital and after three to four hours I feel better,' said Mr Hikmat al-Ugaily, a patient at Ibn al-Nafis.

AP Television News footage showed Iraqi policemen conducting traffic while covering their mouths with scarves, a crippled man in a wheelchair using his clothes to protect himself and others simply running for cover. One enterprising street vendor was seen selling masks.

Airport officials said four flights destined for other Middle Eastern cities were delayed in the morning. Flights resumed in the early afternoon. -- AP