Human rights advocates in Cambodia have called for protection of witnesses who could testify at a UN-backed tribunal for former Khmer Rouge leaders.
More than a million people died under the Khmer Rouge rule
They said intimidation was a major problem and called on the government to guarantee witnesses' safety.
The calls came at a conference in Cambodia's capital, Phnom Penh, on the tribunal that could open this year.
More than a million Cambodians died from starvation, disease or execution under the Khmer Rouge's 1975-79 rule.
"Most of the participants have raised concern over the safety of the witnesses... in the Khmer Rouge tribunal," the president of Cambodia's Licadho human rights group, Kek Galabru, said at the end of the two-day conference.
KHMER ROUGE TRIBUNAL
Will try cases of genocide and crimes against humanity
Five judges (three Cambodian) sit in trial court
Cases decided by majority
Maximum penalty is life imprisonment
Thun Saray, the leader of another local group, Adhoc, suggested setting up "a protection unit for the victims and witnesses".
Concerns for witnesses' safety were shared by the conference co-organiser, the International Federation for Human Rights.
It said that some of the former Khmer Rouge leaders still held significant influence, warning of possible attacks on potential witnesses.
The conference participants also stressed that witnesses must be protected before, during and after their testimony.
Video evidence and closed sessions of the tribunal were among several measures put forward for consideration.
The conference also asked for the tribunal to award some form of compensation to the victims of the Khmer Rouge regime, even if cash reparations were unlikely.
The timing of the tribunal is still uncertain, the BBC's Guy Delauney in Phnom Penh says.
The budget for its three-year duration is $56m (£29m).
But $16m (£8m) still has to be found and proceedings will not start unless all the funds are in place, our correspondent says.