The United States reduced its greenhouse gas emissions by 1.6 percent in 2011 from the previous year, the country's Environmental Protection Agency (EPA) said on Monday.

In a submission to the Secretariat of the UN Framework Convention on Climate Change, the EPA said total emissions of the six main greenhouse gases in 2011, namely, carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride, were equivalent to 6,702 million tons of carbon dioxide.

"This decrease was primarily due to a decrease in the carbon intensity of fuels consumed to generate electricity due to a decrease in coal consumption, with increased natural gas consumption and a significant increase in hydropower used," said the EPA in the annual report.

"Additionally, relatively mild winter conditions, especially in the South Atlantic Region of the United States where electricity is an important heating fuel, resulted in an overall decrease in electricity demand in most sectors."

U.S. President Barack Obama has pledged that the United States would cut emissions by 17 percent by 2020 from 2005 levels, and according to the latest data, emissions fell 6.9 percent from 2005 to 2011.

But for most countries, 1990, rather than 2005, is the base year. Compared with 1990, U.S. emissions are up about eight percent, according to the latest data.