Under ambitious plans to tackle climate change, the EU requires airlines to gradually increase the amount of so-called sustainable aviation fuel (SAF) they use to power planes.

Airlines, however, complain that SAF is not widely available and too expensive.

"I've been critical of the EU targets because I don't think they're going to be achieved," International Air Transport Association director-general Willie Walsh told reporters in Singapore.

"I struggle to see how we will have sufficient sustainable aviation fuel available to meet the near-term target."

EU rules require carriers to include two percent of SAF in their fuel mix starting this year, rising to six percent in 2030 before soaring to 70 percent from 2050.

But a study published by Airlines for Europe, an industry group representing 17 carriers, estimated that SAF production would be 30 percent below levels necessary to achieve the goal in 2030.

"I think the EU in particular needs to reevaluate the targets that they've set," Walsh said, adding however that the industry target of net-zero emissions by 2050 was still achievable.

He said IATA had been reluctant to the idea of setting some near-term targets.

What the EU should have been doing was to assess the current and future production of green fuel "and then set a target relevant to the production", according to Walsh.

"The idea that we're setting targets when we're not seeing the production of sustainable fuel makes no sense whatsoever," he said.

Walsh said individual airlines in Europe "are buying SAF outside of the EU to comply with their targets", which he said also "doesn't make an awful lot of sense" because of the carbon footprint generated by transporting the fuel.

Contributing to almost three percent of carbon dioxide emissions globally, the aviation sector is among the toughest to decarbonise.

SAF -- a biofuel that produces lower carbon emissions than traditional jet fuel, made from plant and animal materials like cooking oil and fat -- is seen as a crucial ingredient to hitting emissions targets.