Red Bull Racing says that it has entered next year's F1 world championship despite still being unclear on what engine, if any, it will have in the back of its cars.

With approaches to both Ferrari and Mercedes having been rebuffed, and a potential tie-up with Honda apparently stalled by McLaren's Ron Dennis, Red Bull is facing the prospect of returning to Renault, the partner it apparently spurned, with its tail between its legs in order to guarantee its place on the grid.

Rumours in the Interlagos paddock suggest that progress is being made in that direction, with speculation that RBR will use a Renault V6 block in conjunction with parts designed by renowned engine guru Mario Ilien, creating what some have already branded a 'super-Renault'.

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While chief engineer Paul Monaghan would not, or could not, confirm whether the team was close to sealing a deal - 'You'll know when we do' were his words - he also remained optimistic that the team would not miss next February's opening pre-season test.

"We are working towards a deal and, if one can be achieved, it'll be announced in time but we'll still make it [to the test], don't worry," he insisted.

Red Bull is clearly confident that it will have sorted its problems before the start of next year's campaign, with Christian Horner telling Sky Sports News that the team had indeed lodged an entry for 2016.

"We've entered the world championship," Horner confirmed, before adding the caveat that "so as long as we sort our engine predicament out, absolutely we'll be there next year.

"As soon as we've got something to say, we'll let you know. Anything else at the moment is just speculation. All I can tell you is we're homing in on something and, as soon as we've got something to announce, you'll be at the top of the list."

Interestingly, it appears that Red Bull and sister team Toro Rosso may once again diverge in terms of power unit, with the Italian-based operation reverting to Ferrari power with use of a year-old V6 package from Maranello. Confirmation of both teams' power source is expected at the Abu Dhabi Grand Prix in a fortnight's time but, for now, STR's Franz Tost was playing his cards as close to his chest as both Monaghan and Horner.

"V6 turbo engine, new regulation," was all the veteran team boss was giving away when asked about Toro Rosso's plans for 2016.