Total emissions amounted to 7.15 billion metric tonnes, the agency's Energy Information Administration said.

The agency said this was well below the annual average since 1990 of 1.0 percent growth in greenhouse gas emissions, blamed for global warming.

US officials argue that despite the high level of overall emissions, the US portion of greenhouse gases is low when measured against economic output.

The report said emissions fell from 664 metric tonnes per million dollars of output in 2004 to 647 in 2005, a decline of 2.5 percent. The measurement is based on the value of the dollar in 2000.

"The 2005 emissions increase is well below the rate of economic growth of 3.2 percent and below the average annual growth rate of 1.0 percent in greenhouse gas emissions since 1990," the EIA said.

"Emissions of carbon dioxide from energy consumption and industrial processes, which have risen at an average annual rate of 1.2 percent per year since 1990, grew by only 0.3 percent in 2005.

"Slow growth in carbon dioxide emissions from 2004 to 2005 can be attributed mainly to higher energy prices that suppressed energy demand, low or negative growth in several energy-intensive industries, and weather-related disruptions in the energy infrastructure along the Gulf Coast that shut down both petroleum and natural gas operations."

Some 84 percent of the emissions were carbon dioxide, with 8.6 percent and 5.1 percent nitrous oxide.

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