World champion Lewis Hamilton believes Honda's gains in Formula 1 have given Red Bull an engine that is now more powerful than Mercedes' in some places.
Red Bull has become a regular challenger at the front of the field since the start of the season and through Max Verstappen has won two of the previous three races.
Hamilton said he is convinced gains made by Red Bull and Honda have surpassed those made by his outfit, and that at venues that particularly suit the Red Bull package it has all it needs to beat Mercedes.
"We're in obviously the period of time where it suits them - and also people need to remember that sometimes a car's better in other places," explained Hamilton.
"A car is not always the best through the whole season. In Austria, Red Bull was a better package for that circuit. It worked well in the temperatures and everything. Even compared to us with a good car, and against the Ferrari.
"It might be that way this weekend. I think Singapore will be strong for them. And when we get to the longer places like Monza, it could be different this year now they have a new power unit.
"They're not lower on power. I think in some places they've got more power than us, so it will be interesting to see how they go in those other races."
Verstappen played down his own chances of fighting for the world championship after his second win of the season at Hockenheim, but has also not totally given up on his bid.
Hamilton insisted it was not a surprise that Red Bull has shown race-winning pace so soon after its switch to Honda power for 2019.
"I think what people need to remember is that it's a multi-championship-winning team, they've always had a very good car," he said.
"You've got Adrian Newey there, who is one of the best designers there is in the sport.
"They had a slump with a little bit less power, then they had a period of time when they had a little bit less downforce than most people. But that definitely crept back up and they have started to utilise this car more.
"Both drivers are now starting to put in good performances. The second driver is starting to put in good performances - so, they're there, and it is clearly a very good car."