The European Union will press ahead with plans to include aviation in its emissions trading system despite United States' efforts through a U.N. body to discourage it, a spokeswoman for the EU executive said on Friday.

Airline emissions are at the top of the agenda of a tri-annual meeting of the International Civil Aviation Organization (ICAO) in Montreal, which began earlier this week.

The United States, which opposes EU plans to include foreign airlines in its emissions trading scheme, is pushing ICAO to let individual nations decide the best way to manage greenhouse gas emissions from their airlines, a U.S. working paper says.

It asks the group to "endorse guidance material for emissions trading that is on that basis of mutual consent" and to say "the only acceptable manner for managing emissions from international aviation is on the basis of mutual agreement."

But the European Commission, which authored the legislation that would include flights coming into and out of the 27-nation bloc from 2012 in the EU scheme, said it will go forward with its proposal, which it says is in line with international law.

"The mutual consent approach for us is not an option," said Barbara Helfferich, spokeswoman for Environment Commissioner Stavros Dimas.

She said ICAO conclusions in 2001 and 2004, which supported establishing a global emissions trading scheme for aviation, had helped spur the EU to get a system started.

"ICAO seems to be wavering on their previous conclusions, which we believe would undermine their own credibility," she said.

Environmentalists say the airline industry must contribute more to reducing the gases blamed for global warming.

"After a shameful decade of inaction and obstruction ICAO must now give its full support to emissions trading and other measures to combat rapidly growing aviation emissions," said Joao Vieira of Brussels-based Transport & Environment (T&E) in a statement earlier this week.

"The EU must be prepared to go it alone should ICAO give anything less than full backing to the emissions trading plan."

T&E said ICAO's guidance on emissions would not be legally binding, but the EU has committed itself in the past to act within the ICAO framework.

Industry positions are mixed. The Association of European Airlines, which represents big carriers such as British Airways and Lufthansa, supports the EU scheme but would prefer a global one, a spokeswoman said.

Global airlines group IATA, which stresses that airlines account for only 2 percent of world carbon dioxide (CO2) emissions, has called for a voluntary but global scheme.

The EU trading system, which began in 2005 for energy intensive businesses such as power companies and oil refineries, sets limits on the amount of CO2 factories may emit.

Companies that overshoot their targets must buy permits in the market or pay a fine, while those that come in below their limits can sell the extra allowances.

Climate change U.S.