Sam Rainsy recently filed a complaint in the state of New York accusing Hun Sen of collusion in a 1997 grenade attack on an opposition rally, which killed 16 people and injured nearly 100, including one American.

Prior to those incidents, when Cambodia was occupied by Vietnam, he said, civilians and children were forced to the front lines in Cambodia's civil war, where they cleared the forests and were injured by land mines or fighting. Such acts constitute crimes against humanity, he said.

“There was conscription of civilians to clear the forest, living and working in areas with malaria and land mines,” he said. “That's a criminal policy.”

CPP lawmaker Cheam Yiep dismissed the allegations. During the 1980s, the country was at war with the Khmer Rouge and needed people's help building barricades, assisting the Vietnamese troops and laying mines, he said.

“The volunteer Vietnamese soldiers were like brothers,” he said. “They helped us because we did not have weapons in our hands and had no army.”

He said there is no evidence linking the CPP leadership to crimes that Sam Rainsy has alleged. Hun Sen “does not have any involvement in those issues.” Cheam Yiep said the 2008 election, which the CPP won in a landslide, had been a determination of justice by the public.

“Sam Rainsy has the right to file complaints in the US court, to any courts, even to God, but they will not be able to interfere in Cambodia's internal affairs,” he said.

Sam Rainsy said Monday he was collecting evidence from widows, orphans and the disabled in preparation to file in court.

“Even if it was a long time ago, the courts have the capability to receive complaints [for killings],” he said, citing the arrest of the leaders of Fiji and Panama accused of similar crimes.

Sam Rainsy is currently in exile, facing a prison of 12 years on forgery, disinformation and incitement charges related to public claims he has made of Vietnamese border encroachment. He is currently traveling in the US and will stop next in Canada, where his party is expected to hold a congress.