Red Bull has reiterated its threat to quit Formula One at the end of the season if it is not provided with a competitive engine.

The team, based out of Milton Keynes, is in discussions with Ferrari over a deal to use its power units in 2016.

But Red Bull, which won four consecutive driver and team championships between 2010 and 2013, will only remain on the grid if the Italian team supplies an engine on par with those used by Sebastian Vettel and Kimi Raikkonen. Toro Rosso, Red Bull's junior team, also faces removal from the sport.

"Red Bull would like to continue in F1 only if Ferrari is willing to provide true works engines that are on the same level as the engines of Vettel and Raikkonen"

Team principal Christian Horner said in Singapore that the threat of Red Bull withdrawing from Formula One should not be "underestimated".

Renault, Red Bull's current engine supplier, is set to end its fractious relationship with the team at the end of the season.

An article, published in Red Bull's media title Speedweek, reads: "For those among us who have listened closely to what Red Bull chief Dietrich Mateschitz and his motor sports consultant Dr. Helmut Marko said recently and who interpret it correctly and put together one and one, a clear scenario emerges: Red Bull Racing and Scuderia Toro Rosso will pull out of Formula One after the 2015 season.

"Red Bull doesn't want to have customer engines that have 30 to 40 bhp less and can be manipulated by the constructor in case of the customer team endangering the works team.

"Red Bull would like to continue in F1 only if Ferrari is willing to provide true works engines that are on the same level as the engines of Vettel and Raikkonen."

Mateschitz, the team's outspoken Austrian owner, who is quoted in the same article, added: "As a customer team you will only get an engine that is good enough to take away points from their immediate rivals.

"But this engine will never be good enough to beat the works team. With such a customer engine we will never be world champion again. And if that's the case we lose interest."

Red Bull had been in talks with Mercedes over using its power units next season. But the Silver Arrows, which boasts the most competitive engine in the sport, withdrew from negotiations a fortnight ago. On Thursday, Toto Wolff, Mercedes motorsport boss, explained the decision.

"We decided with our board that we as an engine supplier - and as a team - have worked hard and long to achieve the success we have today, after taking the decision to enter the sport again as a works team in 2010," he told Formula1.com.

"Therefore we decided two weeks ago against exploring an engine supply to Red Bull.

"We wish to continue with our model to support independent, privateer racing teams - and to respect the relationships we already have in place with our customers - alongside our primary focus on the Mercedes works team."