The chief ideologist and “Brother Number Two” of Cambodia’s Khmer Rouge has died at the age of 93, a court spokesman says.

Nuon Chea was found guilty of genocide by a UN-backed court and sentenced to life in prison last year, almost four decades after the Maoist regime that oversaw Cambodia’s “Killing Fields” was overthrown.

The Khmer Rouge’s brutal rule in the 1970s led to the deaths of some two million people.

Chea was among a small clique – led by “Brother Number One” Pol Pot – of mostly French-educated communists who rose to lead a bloody revolution against a US-backed government after their country was engulfed by the Vietnam War.

The extremist ideology of the 1975-79 regime sought to turn Cambodia back to “year zero” in its quest for a peasant utopia.

Between 1.7 and 2.2 million people, almost a quarter of the South-East Asian country’s population, died during its four-year rule.

People died from starvation, torture, exhaustion or disease in labour camps, or were bludgeoned to death during mass executions.

Researchers believe Nuon Chea was responsible for the murderous policies of the Khmer Rouge, and was directly involved in its purges and executions.

“We can confirm that defendant Nuon Chea, 93, passed away this evening on 4 August 2019 at Khmer Soviet Friendship hospital,” Extraordinary Chambers in the Courts of Cambodia spokesman Neth Pheaktra said on Sunday.

“Nuon Chea’s family has been informed.”

Pictures of four senior Khmer Rouge figures, including Nuon Chea, during a 2011 trial. Photo: Getty

Mr Pheaktra did not say how Chea died, but said he had been in hospital since early July.

Of the Khmer Rouge’s leaders, only former president Khieu Samphan and Kaing Guek Eav, also known as Comrade Duch, are serving life sentences after being convicted of genocide and crimes against humanity.

Khieu Samphan and Nuon Chea were found guilty of crimes against humanity in the first phase of the complex UN trial and sentenced to life in prison in 2014.

A separate trial last year found Chea guilty of genocide.

Pol Pot died in 1998 at the age of 73.

-AAP