LE CASTELLET, France (REUTERS) - Mercedes dominated French Grand Prix practice on Friday (June 21) with Formula One championship leader Lewis Hamilton and team mate Valtteri Bottas each top of the timesheets in soaring temperatures.

Ferrari, whose attempt to overturn the result of the previous Canadian race and have Sebastian Vettel restored as winner was later dashed by stewards, were once again the best of the rest.

Race favourite Hamilton, a late arrival at Le Castellet after attending a memorial for fashion designer Karl Lagerfeld in Paris on Thursday, lapped the Paul Ricard circuit in one minute 32.738 seconds in the first session.

Bottas, second fastest, turned the tables on the five-times world champion in the afternoon with a lap of 1:30.937.

"It's been very hot today, but we got through most of the programme," said Hamilton, who is 29 points clear of Bottas after seven races.

"It's been a bit difficult with the balance of the car; maybe that's to do with the new tarmac they have here and the high temperatures, I think the track reached 55 to 60 degrees today," added the Briton.

Hamilton ran off track after the car snapped and spun into turn three in the afternoon when he was on a soft tyre run, with the team then detecting a misfire in his car's power unit.

He ended the session under investigation after rejoining the track ahead of Red Bull's Max Verstappen but stewards took no further action.

Ferrari's Charles Leclerc was third fastest in both sessions, with Sebastian Vettel fifth and fourth respectively on a sunny day in the south of France.

Mercedes have won all seven races so far this season, and nine in a row in total.

The cornering areas of the track have been recently resurfaced and Bottas said it was more slippery than usual in the morning.

"We've made good changes between the sessions and I felt much more comfortable in FP2 (the second session), which is why the lap time was better," said the Finn.

"It's really warm out there, and it will only get warmer, so tyres are going to be on the limit, especially on Sunday."

Verstappen was fourth in the morning, his car benefiting from a Honda engine upgrade, but slipped back to sixth after lunch.

French driver Romain Grosjean missed much of the first session, completing just nine laps, after a water leak to his Haas.

Hamilton won from pole last year when the French Grand Prix returned after a decade's absence.