BEIJING -- China's environmental watchdog has suspended environmental approval for refining and chemical projects by the country's two oil and gas giants due to their weak environmental protection performance.

The China National Petroleum Corporation (CNPC) failed to meet the reduction target for chemical oxygen demand emissions in the 2012 annual evaluation on reduction of major pollutants, the Ministry of Environmental Protection statement said Thursday.

The China Petroleum and Chemical Corporation (Sinopec) failed to reduce targeted emissions of nitric oxide, according to the statement.

CNPC, Asia's largest oil and gas producer, failed to meet the target for reducing chemical oxygen demand emissions in the 2012 annual evaluation on reduction of major pollutants, the statement said.

Sinopec, China's largest oil refiner, failed to reduce targeted emissions of nitrogen oxide, according to the statement.

It added that energy-saving projects and projects concerning the upgrading of oil products are excluded from the suspension.

The ministry said the punishment will not affect China's domestic oil refining capacity and oil supplies.

It said when the suspension will be removed depends on assessments of the two companies' performance in emissions reduction in the first half of this year.

The central government required CNPC and Sinopec to reduce their emissions of nitrogen oxide by 8 percent by the end of 2015 as compared with that in 2005. Instead, by the end of 2012, such emissions surged 8.27 percent for CNPC and 2.52 percent for Sinopec, according to the ministry.

It said poor industrial facilities contributed to the companies' high emissions of pollutants.

The CNPC has 115 coal-fired boilers, 38 of which are not equipped with desulfuration facilities. None of its boilers are equipped with denitration facilities.

Among the 174 coal-fired boilers used by Sinopec, 69 are not equipped with desulfuration facilities and only four are equipped with denitration facilities.

The nation's chemical oxygen demand emissions reached 24.2 million tonnes last year, dropping 3.05 percent year on year, while the amount of sulfur dioxide emissions decreased by 4.52 percent to 21.2 million tonnes, the statement said.

Environmental protection awareness, especially regarding the need to improve air quality, has greatly increased among both the public and authorities.

The central government last year rolled out a five-year plan for reducing overall air pollution, vowing to cut the PM2.5 intensity by at least 5 percent by 2015 in 13 major areas covering 117 cities.

Tough measures have also been taken to ensure the country's fulfillment of the commitment that by 2020 carbon dioxide emissions per unit of GDP would drop 40-45 percent as compared with that in 2005.

The statement said that in 2012 China cleaned up 1.32 million vehicles with high emissions of pollutants and pushed heavily in eliminating outdated production facilities in industries like paper making, printing, steel and cement.