Japan and France urged the U.N.-backed Khmer Rouge tribunal on Tuesday to expedite the trial of the sole surviving senior leader of the 1970s Khmer Rouge regime, after another top figure died over the weekend.

In a joint statement, the embassies of the two countries expressed their regret that Nuon Chea, who was the regime's No. 2 leader, had died Sunday at the age of 93 before the judicial process in the Extraordinary Chambers in the Courts of Cambodia was complete.

"More than ever, it is urgent that every stakeholder of the ECCC fulfills its responsibility so that the trial of the remaining co-accused proceed in a fair, efficient and expeditious manner and that overdue justice be realized in Cambodia," it added.

Nuon Chea, who was the Maoist-inspired regime's chief ideologist, had been tried along with former head of state Khieu Samphan, now 88, for a series of crimes committed during the 1975-79 reign of terror that left more than 1 million people dead.

On Aug. 7, 2014, the Trial Chamber of the ECCC found both men guilty of crimes against humanity and sentenced them to life in prison. The sentences were upheld on appeal in 2016.

In November 2018, the same tribunal convicted them of genocide and other crimes against humanity, handing down life sentences that both of them appealed last month.

Since the hybrid court's inception in 2006, it has tried and convicted only three Khmer Rouge figures.

The third is chief jailer Kaing Guek Eav, who was sentenced to life in prison in 2012 for the deaths of more than 12,000 people at a torture center he ran.

The court has yet to set any date for the final hearing in Khieu Samphan's appeal trial.

Japan and France are co-chairs of the "Friends of the ECCC," which comprises the ambassadors of the principal donor countries.