Fernando Alonso and Stoffel Vandoorne currently have zero points in the 2017 driver standings

McLaren drivers Fernando Alonso and Stoffel Vandoorne will start Sunday's Azerbaijan Grand Prix from the back of the grid after engine penalties.

The sanctions follow a Honda engine upgrade in addition to earlier reliability problems.

Both drivers have already used more than the permitted number of relevant parts after just seven races of 21.

Alonso's penalties total 15 places and Vandoorne's 30, so the Spaniard will start ahead of his team-mate.

Alonso said: "We try to go through the weekend in the best way possible, perform the best we can but there are some things out of our control.

"It will be like this all season long. We used already the maximum engines that we are allowed in the first seven races and now we will start last in a couple of other races.

"That will make things even more difficult but it is the way it is and we can't do anything other than perform at our best."

Some of the penalties arise from the fact that both drivers will use a new design of turbo and MGU-H, the motor-generator unit that recovers energy from the turbo.

As both have already used more than the permitted number of these for the season, they incur a grid drop.

Vandoorne's extra 15 penalty places arise from the fact that Honda is also planning to change his entire power-unit after Friday practice.

Taking a new one will mean a seventh MGU-H and turbo so far this season for the Belgian. Only four are allowed before incurring penalties.

Before this weekend, both Alonso and Vandoorne had already used five turbo/MGU-Hs this season, when only four are permitted for the entire year.

Honda is also to test a series of new components on the engine in practice on Friday and will decide whether to use those upgrades for the rest of the weekend after analysing the data from the two sessions.

Asked whether the new parts would bring significantly improved performance, Vandoorne said: "Difficult to say, to be honest. I think probably more a question for Honda. I don't think it will be too different."

McLaren are in the process of trying to resolve a divorce from Honda, after losing faith that the Japanese company can ever sort out the reliability and performance problems that have afflicted it since it returned to F1 in 2015.

They are expected to attempt to try to secure a supply of Mercedes customer engines for next season.

Vandoorne said: "We are trying to put McLaren's interests at the top. We need to fight back.

"I am pretty sure the team is moving in the right direction and hopefully at some point we will be competitive again. Hopefully that is sooner rather than later."