Japan's Honda Motor will end its participation as an engine supplier in the FIA Formula One World Championship at the end of the 2021 season to focus on zero-emission technology, it said on Friday.
The decision was made at the end of September, and the company does not intend to return to F1, Chief Executive Takahiro Hachigo said in an online news conference.
"This is not a result of the coronavirus pandemic but because of our longer-term carbon-free goal," he said.
The Japanese carmaker supplies two Red Bull-owned F1 teams – Red Bull Racing and Italy-based AlphaTauri (previously Toro Rosso).
Both teams have been Grand Prix winners this season, making Honda the only engine supplier to have won with two different teams in the V6 turbo hybrid era that started in 2014 and that has been dominated by Mercedes.
"We understand how difficult it has been for Honda Motor Company to reach the decision. We understand and respect the reasoning behind this," Red Bull Team Principal Christian Horner said in a statement.
Honda's departure will leave only Mercedes, Ferrari and Renault as Formula One engine makers.
Horner said Red Bull, whose main driver is highly-rated Dutch 23-year-old Max Verstappen, would evaluate their options as a group.
Red Bull won four constructors' titles in a row with Renault from 2010-13 but the relationship with the French manufacturer soured in the V6 era, with the team branding the engines as Tag Heuer for a period.
Both Red Bull-owned teams have used Ferrari units previously, but the Italian manufacturer's power unit has lost performance this season.
Mercedes already supply Racing Point and Williams as well as their own factory team and are due to provide engines to McLaren, currently with Renault, next year.
"Whilst we are disappointed not to continue our partnership with Honda, we are enormously proud of our joint success, delivering five wins and 15 podiums for both Red Bull-owned teams," said Horner.
He said Red Bull remained committed to the sport in the long term, having recently signed a new commercial agreement for the next five years.