Red Bull's former chief designer Adrian Newey has hit out at engine manufacturers Renault.
The former constructors' champions suffered multiple engine issues last season, and their 2015 campaign has got off to a bad start as Daniel Ricciardo managed only seventh on the grid in Australia.
Reports have suggested that this season's Renualt engine is down on power in comparison to those of Mercedes and Ferrari, and Newey has claimed that their relationship with Red Bull is strained.
He told The Telegraph: "We keep trying to offer help and try to be involved but there seems to be a real reluctance to engage. It's one thing being in the position where you're not competitive but you can see your way out of it. It's another thing when you're not competitive and your partner doesn't seem to be willing to engage. I honestly don't know the reason for it.
"In pre-season testing, we had 12 days and a filming day in which I think we had six major failures. So our mileage was very restrictive through engine problems."
Newey added: "It's very frustrating that we've been pushed into a position where we've got an engine which is quite a long way behind with no obvious light at the end of the tunnel with all sorts of failings."
The new season gets underway tomorrow morning with the Australian Grand Prix in Melbourne.
