Heavy air pollution in Mongolia's smog-filled capital has caused flight delays and cancellations in recent days, an Air China official said Tuesday.

During the last week, many flights were disrupted for six days except Thursday. And a total of 13 flights had been delayed or canceled this month due to air pollution, a 160-percent increase compared with the same period of last year, according to statistics provided by Air China.

With temperatures dropping sharply in December, thousands of residents living in ger districts near the airport have begun to burn large quantities of coal and firewood to get warm, and power plants are also operating at full steam to meet high demand for electricity for heating, causing a thick smog around the airport, said the official from Air China's Mongolia Bureau.

"Ulan Bator as well as the airport are located in a basin with mountains surrounded, so the smoke is blocked by the mountains and cannot dissipate. Wind also is very rare during winter time which worsens the air pollution here," the official said.

In recent years, more and more people from rural areas have rushed into the capital seeking better lives, making the city increasingly crowded.

The new residents live in ger districts in the suburbs, and due to the lack of access to central heating systems, they burn coal, firewood and garbage, which causes severe air pollution.

Air pollution kills about 1,600 people in Ulan Bator every year. A report released this month by the World Health Organization showed that the concentration of dust particles in the air was 35 times the standard recommended by the WHO.