The genocide trial of two former Khmer Rouge leaders has resumed at a UN-backed court in Cambodia where they face charges over the mass murder of Vietnamese people and ethnic Muslims, forced marriage and rape.

Nuon Chea, 88, known as Brother Number Two, and ex-head of state Khieu Samphan, 83, have already been given life sentences after a separate trial at the same court in August for crimes against humanity.

That ruling saw them become the first top figures to be jailed from a regime responsible for the deaths of up to 2 million Cambodians from 1975-1979.

The second trial, which opened in July, got under way on Friday with judge Nil Nonn reading out the charges against both suspects of genocide, crimes against humanity and war crimes.

Nuon Chea, wearing his familiar sunglasses, and Khieu Samphan sat in court alongside their defence teams as about 300 survivors of the regime protested outside, demanding monetary compensation for their suffering.

The complex case against the pair was split into a series of smaller trials in 2011 to get a faster verdict given the vast number of accusations and their advanced age.

Both men have appealed against their August convictions, which followed a two-year trial focused on the forced evacuation of around 2 million Cambodians from Phnom Penh into rural labour camps and murders at one execution site.

The second trial, broader in scope than the first, is viewed as an opportunity for many other victims of the regime to seek redress.

The mass killings of an estimated 100,000 to 500,000 ethnic Cham Muslims and 20,000 Vietnamese form the basis of the genocide charges against the pair.

“The ways in which the Khmer Rouge mistreated us is too heinous to describe in words. Their goal was to exterminate our race,” said Seth Maly, a 64-year-old Cham labour camp survivor who lost 100 of her relatives, mostly through execution, during the regime – including her two daughters, parents and five siblings.

Nuon Chea and Khieu Samphan also face charges of crimes against humanity and war crimes in the second trial – for the deaths of up to 2 million people through starvation, overwork or execution during the communist regime.

A court spokesman has estimated the trial may go on until 2016.