The European Union and 16 surrounding countries including Turkey, Ukraine and Georgia say they will join the first phase of a UN-brokered deal to limit carbon emissions from international flights, following a similar pledge by China and the United States.
The United Nations' International Civil Aviation Organisation (ICAO) meets from September 27 to October 7 to finalise the deal, which would aim to cap the carbon pollution of all international flights at 2020 levels.
Aviation was excluded from last December's climate accord in Paris when countries agreed to limit the global average rise in in temperatures to "well below" 2 deg C above pre-industrial levels.
The proposed new deal on aviation will be voluntary between 2021 and 2026 and then mandatory from 2027 for the world's largest emitters.
Airlines in participating countries would need to limit their emissions or offset them by buying carbon credits from designated environmental projects around the world.
The European area announcement generates momentum for the deal which has faced scepticism from EU lawmakers concerned that a voluntary first phase which allowed countries to opt out was not ambitious enough.
The European Civil Aviation Conference (ECAC), a grouping of the EU and 16 other countries, said it would join the market-based plan from the start and urged all other major aviation states to do so.
China and the US, the world's two biggest emitters of carbon from international flights, said earlier on Saturday they would also volunteer for the first phase.
China's participation had been seen as critical to covering around 80 percent of the expected rise in emissions from international flights after 2020.
Mexico, Canada and Indonesia had already said they would join.