Nuclear fusion has the much-vaunted potential to provide the world with clean, safe and nearly inexhaustible energy -- but the scientific holy grail has remained stubbornly elusive over decades.

The idea is to recreate the process that occurs at the heart of stars by fusing two atomic nuclei. This would be the opposite of fission -- which splits the atom -- that is used in nuclear power plants.

Among other things, the process requires temperatures of more than 100 million degrees Celsius to create and maintain plasma.

This hot, electrically charged gas easily becomes unstable, which can lead to lost energy and limit the efficiency of a possible future nuclear fusion reactor.

The WEST tokamak machine in southern France managed to maintain plasma for 1,337 seconds on February 12, France's Atomic Energy Commission (CEA) said in a statement.

This "smashed" the previous record set in China last month by 25 percent, said the CEA, which runs the tokamak machine.

The CEA's head of fundamental research Anne-Isabelle Etienvre told AFP that achieving plasma for that long shows "that we control its production, but also its maintenance".

But there are still many "technological barriers" to overcome before thermonuclear fusion can "produce more energy than it consumes", she added.

In the coming month, the WEST team is aiming to achieve even longer plasma durations -- "up to several hours combined" -- as well as higher temperatures, according to the CEA.

In doing so, the researchers hope to approach the conditions "expected in fusion plasmas", the statement said.

The scientists will also observe the effect that such "intense plasma" has on the inside of their tokamak machine, Etienvre said.

The goal is to prepare the ground for the International Thermonuclear Experimental Reactor (ITER) being built in France, she added.

First set in motion in 1985, the ITER brings together China, the European Union, India, Japan, South Korea, Russia and the United States.

It had been scheduled to go online this year, but repeated setbacks, delays and spiralling costs have postponed operations until at least 2033.