The €20bn ($21bn) International Thermonuclear Experimental Reactor (Iter) nuclear fusion plant under construction at Cadarache in southern France could face “years” of delays, its new boss told AFP.

Fusion entails forcing together the nuclei of light atomic elements in a super-heated plasma, held by powerful magnetic forces in a doughnut-shaped chamber called a tokamak.

Iter’s previously-stated goal was to reach the key milestone of creating the plasma by 2025.

But Pietro Barabaschi, who became the project’s director-general in September, told AFP during a visit to the facility that the deadline will have to be postponed.