A major breakthrough in the search for clean energy has been made by US government scientists at a laboratory in California, it has been reported.

A fusion reaction, carried out at the Lawrence Livermore National Laboratory produced more energy than was absorbed by the fuel to create it.

It represents a major milestone in the drive to wean the US and other major economies from carbon-producing fossil fuels which scientists regard as the main driver of climate change.

The energy crisis triggered by the war in Ukraine has intensified the need for alternative energy.

Earlier this year the Biden administration passed the Inflation Reduction Act, which included nearly $370bn in new subsidies for low-carbon energy.

On taking office, Mr Biden pledged that his administration would be a global leader in the race to develop green technology.

The US energy secretary, Jennifer Granholm and under-secretary for nuclear security Jill Hruby are due to announce the breakthrough on Tuesday.

In August last year, the Livermore laboratory announced the results of a reaction which released 1.3 megajoules of energy, about five times the 250 kilojoules that were absorbed by the capsule.

The reaction is produced by bombarding a minute blob of plasma with light from 192 lasers at the laboratory’s $3.5 billion National Ignition Facility, which was initially created to test nuclear weapons by simulating explosions.

Ms Hruby hailed the results at the time.

“These extraordinary results from NIF (National Ignition Facility) advance the science that NNSA (National Nuclear Safety Administration) depends on to modernise our nuclear weapons and production," she said.

“It also offers potential new avenues of research into alternative energy sources that could aid economic development and help fight climate change."

However, that fell short of the 1.9-megajoule target set by the NIF.

That threshold was breached in recent weeks by scientists at Livermore, the Financial Times reported.

It is understood the latest laser reaction produced 2.5 megajoules of energy. The results of the fusion experiment are still being analysed.

Such was the power produced in the fusion experiment that some of the diagnostic equipment was damaged.

The laboratory has remained cautious, beyond describing the experiment as successful.

“Initial diagnostic data suggests another successful experiment at the National Ignition Facility,” it said.

“However, the exact yield is still being determined and we can’t confirm that it is over the threshold at this time.

“That analysis is in process, so publishing the information . . . before that process is complete would be inaccurate.”

Fusion reactions produce neither carbon nor long-lived, radioactive waste - effectively reaching the holy grail in energy production.

It also enables vast amounts of energy to be produced from very little hydrogen fuel.

The technique of inertial confinement fusion dates back to the 1970s and simply put aims to harness the power found in nuclear weapons to produce energy.

Fusion energy has bipartisan support in Washington.

Earlier this year Democratic congressman Don Beyer, who started the Fusion Energy Caucus, stressed the technology was different from that used to produce power at Fukushima and Chernobyl.

“Fusion is the Holy Grail of climate change and decarbonised future,” he told a White House summit.

“Perhaps even more profoundly, fusion has the potential to lift more citizens of the world out of poverty than any idea since fire.”