Image caption Francois Hollande continues to face pressure to lift the ban on fracking

French President Francois Hollande has again ruled out exploration for shale gas during his presidency.

The comments come as a French court was due to examine an appeal against a government ban on "fracking".

France has some of the most plentiful reserves of shale gas in Europe, but there are objections to shale exploration on environmental grounds.

"As long as I am president, there will be no exploration for shale gas in France," Mr Hollande told French TV.

France's top court was this week due to examine a challenge to the ban on fracking - the process by which shale gas is released - by Schuepbach Energy, which held two exploration permits that were cancelled when the law was passed in 2011.

Supporters of drilling for shale gas say it would help boost the ailing French economy, and they point to the example of the United States where the shale revolution has led to a fall in gas prices.

French Industry Minister Arnaud Montebourg sparked debate when he suggested creating a state-backed company to examine exploration for shale.

But he was promptly overruled by Prime Minister Jean-Marc Ayrault.

And now Mr Hollande has also re-affirmed the government's position.

"The debate on shale gas has gone on for too long," he said.

Scheupbach Energy challenged the ban in the local court of Cergy-Pontoise near Paris, which forwarded the case to France's highest administrative court, which then passed it on to the Constitutional Council.

Hydraulic fracking involves releasing gas trapped in rocks by pumping in water mixed with sand and chemicals at high pressure.

Critics say shale gas drilling can poison underground water and even cause earth tremors.

The technique is used widely in Canada and the US, but has sparked controversy in Europe, including in the UK where shale gas exploration is planned.