Christian Horner insists no decision about Red Bull Racing's immediate future plans have been made despite paddock rumours that it has served a notice of termination with Renault for its engine supply.

With its relationship already fractious on the back of Renault's struggles to develop its underpowered and comparatively unreliable power unit, matters are being exacerbated by the prospect of the French firm purchasing the Lotus team for a fully-fledged manufacturer effort in 2016.

As it stands, Red Bull's relationship with Renault is due to conclude at the end of the 2016 season and Horner says he has assurances that it is contractually obliged to remain its 'priority' team next season.

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However, with Renault's talks seemingly at an advanced stage but ongoing, Red Bull is said to be becoming increasingly uneasy at the lack of a firm decision, with the latest rumours in the paddock suggesting it is seeking to get out of its contract with Renault early in favour of a switch to Mercedes power.

Horner, however, dismissed the notion of the contract termination as simply 'speculation', even if he refused to deny it outright.

"It depends on Renault. We have got an agreement with Renault until the end of 2016 and anything other than that is purely speculation.

"[The termination of contract story is] complete speculation. It's speculative. We've got a contract with Renault with Red Bull Racing and the contents of that contract, I'm not going to disclose publicaly. There are obligations on both parties and I'm not going to comment paddock gossip."

Indeed, Horner says Red Bull is ultimately waiting on Renault to determine its future - which could yet see it leave the sport altogether - before it can forge its own plan going forward.

"I think the bigger danger is if we don't manage to address out current situation, the damage will be significant. We've heard Dietrich comments earlier in the year, it's important not to take that too lightly. We have to address the competitiveness of the team moving forward.

"Our priority is obviously on the second half of this year, we want to hear what Renault's plans are for the future and what that entails, whether that's as an engine supplier or a team owner, they've got to have a competitive engine unless they decide to stop and once we understand that then we can make a plan."