Red Bull and Honda have scheduled further talks for the Spanish Grand Prix, amid growing indications they could join up in Formula 1 in 2019.
As Autosport revealed earlier this week, the Milton Keynes-based team and the Japanese manufacturer held their first formal discussions about a potential future engine partnership in Baku last weekend.
There, Red Bull motorsport advisor Helmut Marko sat down with Honda motorsport boss Masashi Yamamoto to map out initial ideas about what could be possible from next year.
It has since emerged that the talks were encouraging enough for a second round of negotiations to be firmed up for the next race at Barcelona, which Yamamoto will attend.
Sources have suggested both sides are pushing hard for a Red Bull-Honda deal to be sorted - with the Canadian Grand Prix in June potentially key to a final decision as both Honda and Red Bull's current supplier Renault are set to introduce engine upgrades for that race.
Red Bull is keeping tight-lipped on the state of negotiations, but has suggested it is waiting for Honda's latest upgrade so it can judge its full potential.
"We are very satisfied with the way the partnership with Toro Rosso is going," Marko told Autosport.
"The reliability has already improved considerably. And as far as performance goes, we'll wait for the next update."
Red Bull's desire to wait until Canada before making a decision would put it beyond the preferred May 15 date that Renault has favoured, so it is unclear how the French manufacturer would respond if there was no commitment by that date.
Although it is understood that any Red Bull-Honda alliance will not result in the kind of financial injection to the team that McLaren enjoyed, there is scope for a stronger alliance than just being engine partners.
Honda is eager to get one of its junior drivers in to an F1 seat, which would most likely be with Toro Rosso.
The obvious candidate for this is Nirei Fukuzumi, who is running a joint campaign in Formula 2 and Super Formula this year to help boost his F1 superlicence points potential.
A Fukuzumi promotion to Toro Rosso would mean that one of the team's current drivers Pierre Gasly or Brendon Hartley would have to move aside.