UN Secretary-General Ban Ki-moon nominated Kasper-Ansermet to replace a German judge who resigned last year.
The Documentation Center has collected nearly 1 million documents on the Khmer Rouge since 1995.
Kasper-Ansermet was to have filled a vacancy created by the departure of German judge Siegfried Blunt - who resigned late last year.
A UN spokesman told VOA Khmer this week the government has an obligation to fill vacant posts at the court.
The UN appointed a reserve judge to the position, Laurent Kasper-Ansermet, but that appointment has not been confirmed.
This comes a day after defense attorneys say they want to summon the head of a leading genocide research organization before the court.
The Documentation Center has provided around 500,000 documents to the tribunal since its inception.
Jailed Khmer Rouge leader Khieu Samphan refused to answer questions from the UN-backed tribunal on Thursday.
A UN spokesman said the organization was “aware of this development” but declined to comment further.
Nuon Chea’s portion of the hearing lasted just a half a day Tuesday.
The dueling public statements further underscore ongoing divisions at the court, which has come under heavy criticism in recent years.
Over the year, nearly 110,000 people sat in on court proceedings to observe the trial process, Huy Vannak said.