The United States embassy in Malaysia today warned its citizens to don masks and stay indoors after a choking haze enveloped the nation's capital and surrounds.

The embassy said in a statement distributed to residents and visiting Americans that air quality conditions in Kuala Lumpur "have been particularly poor lately".

It listed five dates in August - the 3rd, 4th, 8th, 9th and 10th - where there had been up to nine hours in which the air quality was either unhealthy or very unhealthy.

"The Embassy Health Unit has seen a significant increase in respiratory problems, sinusitis and bronchitis in the past few days," it said.

"The embassy is mandating that employees who are required to work outside wear masks and limit outside activity as much as possible."

It added that it was trying to determine how long the pollution would last and the likely future air quality levels, and called on Americans to monitor the situation.

Eight-year ban lifted

Until today the Malaysian government had observed an eight-year ban on releasing air pollution index (API) figures, but finally backed down due to growing public pressure to make the information available.

It showed that the API in Kuala Lumpur at midday today was 181 and the southern suburb of Shah Alam was at 316, while the major shipping area of Port Klang in the country's west hit 410.

Under the air quality index, less than 50 is good, 51-100 is moderate, 101-200 is unhealthy, 200-300 is very unhealthy and more than 300 is hazardous.

The haze crisis is being blamed on peat fires outside Kuala Lumpur, as well as hundreds of blazes in Indonesia's Riau and North Sumatra provinces.

In 1997 and 1998 choking haze caused mainly by Indonesian forest fires enveloped parts of Southeast Asia including Malaysia for months, causing an estimated 9.3 billion dollars in economic losses to the region.