BEIJING - A lax enforcement of the law has allowed more construction dust than usual to pollute the city's air, an environmental watchdog said on Monday.

The Beijing Environmental Protection Bureau said that has been in part responsible for the hazy days that have roused the public to anger in the past month.

On Friday, the bureau issued a warning to 17 construction sites that had failed to bring their release of construction dust under control, asking them to eliminate the violations in three days.