Pollution in Beijing (undated photo)

China has started enforcing stricter vehicle emission standards in Beijing to cut pollution ahead of the Olympic Games in August.

As of January 1, fuel sold in the capital city must meet standards equivalent to those in the European Union.

Chinese officials say the earlier fuel standards, introduced at the end of 2005, already cut sulfur dioxide emissions by almost 2,500 tons per year. The new standards are aimed at reducing annual emissions by an additional 2,000 tons.

China is trying to allay international concerns that its serious air pollution may affect athletes' performance and health at the summer Olympic Games this year.

Beijing, which is one of the world's most polluted cities, says it has improved air quality so that it meets Chinese standards 70 percent of the time.

On Monday, the last day of 2007, officials in Beijing said the city had 246 so-called "blue sky" or clean-air days, surpassing the target for the year.

Critics say that what is considered clean air in Beijing amounts to polluted air by international standards.

Some information for this report was provided by Bloomberg and Reuters.