A UK watchdog on Wednesday banned three online adverts from airlines Air France, Etihad Airways and Lufthansa for "misleading" claims over their environmental impact.

The Advertising Standards Authority (ASA) said the announcement was "part of a wider piece of enforcement work on climate change and the environment" as it cracks down on greenwashing or misleading climate-related statements designed to boost company reputations.

The ads, which were all published on Google in July, stated Air France was "committed to protecting the environment" and urged customers to "travel better and sustainably".

Lufthansa meanwhile indicated that travellers choosing the German airline would "fly more sustainably", while Etihad claimed it offered "environmental advocacy" to passengers.

The ASA ruled that the advertisements failed to show the impact all three airlines have on the environment and on the climate.

The regulator said Air France did not provide a "substantive response" to its investigation.

The airline told AFP that the ad "was generated by an artificial intelligence tool based on keywords entered by a user".

"This targeted ad was only visible online from the UK, and only 80 people saw it," it added.

"As soon as the ASA's decision was announced Air France changed the parameters for creating online advertisements to ensure that such an event could not happen again."

Lufthansa told AFP that its advert had referred to its so-called "green fares" option, whereby flights can use sustainable aviation fuel and offer carbon offsetting to lower emissions.

The German carrier "regrets that the Google advertisement in question lacked the explanation," it said in a statement.

Etihad said it had subsequently removed all references to "environmental advocacy" from its Google adverts.

The ASA, which said the offending ads were picked up by its own AI software to identify possible rule-breakers, added on Wednesday that air travel clearly impacted climate change.

"We understood that air travel produced high levels of both CO2 and non-CO2 emissions, which were making a substantial contribution to climate change," the watchdog stated.

"We also understood that there were currently no initiatives or commercially viable technologies in operation within the aviation industry that would adequately substantiate absolute green claims."