Valtteri Bottas topped the times to maintain Mercedes supremacy when the third and final practice for the French Grand Prix was severely curtailed by a heavy rainstorm on Saturday.

The Finn clocked a best lap of the tricky Le Castellet circuit in one minute and 33.666 in the opening eight minutes before rain swept across the track.

That was enough to lift him 1.2 seconds clear of Carlos Sainz of Renault and well ahead of highly-rated Monegasque driver Charles Leclerc of Sauber and Fernando Alonso, who was fourth for McLaren.

Championship leader Sebastian Vettel of Ferrari was fifth ahead of Stoffel Vandoorne in the second McLaren and Frenchman Pierre Gasly of Toro Rosso.

Defending four-time champion Lewis Hamilton of Mercedes, who trails Vettel by a single point, was 12th, but did not attempt to clock a meaningful lap time. Hamilton was fastest in both sessions on Friday.

The rain relented with nine minutes remaining to allow a number of drivers to venture out and test the conditions with 'wet' tyres, but it had little relevance to the outcome.

After several days of heat-wave conditions, heavy thunderstorms are forecast to continue on Sunday when the first French Grand Prix for a decade, and first at Le Castellet's 'Paul Ricard' circuit in 28 years, is scheduled to start.