Renault has confirmed that it has made a firm offer of a power unit supply for Red Bull for 2017.
Motorsport.com revealed after the Russian Grand Prix that the French car manufacturer was pushing to continue its relationship, and has now revealed that formal notification has been made.
Under the recent FIA agreement, manufacturers have until May 15 to inform the FIA of what teams are contracted or have an offer for next season.
Only if a team has no offer will an obligation to supply procedure, via which the FIA effectively brokers a deal, come into play.
The Renault offer means that its focus will now be with Red Bull, with negotiations likely to advance quickly.
Renault F1 managing director Cyril Abiteboul told Motorsport.com: "I think you can say that Red Bull has an offer.
"Frankly if you had asked me this time last year I would have been absolutely unable to answer accurately. It's not exactly the same situation, but it's also quite difficult to bet on a potential outcome from commercial discussions in this environment, which is F1.
"What I can observe is the relationship between Renault and Red Bull Racing is better. It has improved, on the back of the improvement of our product.
"I would hope and expect that if we continue to demonstrate that the product that we deliver can be improved, and can become also the type of engine that you need to be fighting for podiums and even championships, that there will be a mutual interest to continue."
Abiteboul added that the timing of the major upgrade for Montreal – which will be tried on track in next week's Barcelona test – could help to move discussions along, and could help convince Red Bull that things are going in the right direction.
"There is an obvious relationship that can continue. If that principle is agreed, which is not the case now, then it will be about agreeing the figures," he said.
"Red Bull is absolutely more than welcome to remain a customer of Renault. To be more specific, it's my wish, my desire.
"Now we need to deserve it from a technical and competitive perspective, through our product. It's what matters to Red Bull, and actually the test where we run the new spec is coming at just the right moment.
"It's just a bit late for May 15, but that's actually the point of making an offer prior to having an agreement. Red Bull have a binding offer from us."
Although last year Renault was weighing up if its F1 future was better spent being focused on its works team, Abiteboul says that having customers is now appealing.
"I've always said that if strategically it's interesting to continue to have customers - and why not Red Bull Racing - we should do so," he said. "We didn't burn bridges last year.
They are extremely helpful in what we are doing, in particular on the engine side, but also to benchmark the chassis. Strategically, it's good. They need an engine, so why not?"
Toro Rosso future
Abiteboul did also not rule out a return to Toro Rosso, given that when both Red Bull-owned teams have the same engine there is a lot of potential crossover.
"We are open for business, we are pragmatic. When I say the bridges are not burned it's with Red Bull in its entirety.
"We clearly didn't do a good job last year with Toro Rosso, so I can expect some resistance from Toro Rosso, but as I said we are open for business.
"I would imagine that the reasons why it made sense for Red Bull to have the same engine on the two teams remain valid, but it's completely their decision. It's not a condition for us, but anything is possible in F1."