Chea left, Samphan right

In this report:

• Civil unrest feared
• United Nations considers tribunal
• Honor among thieves?

PHNOM PENH, Cambodia (CNN) -- Cambodian King Norodom Sihanouk said Monday he would be willing to give up his royal and constitutional immunity to appear before any court created to judge the Khmer Rouge and he would accept any prison sentence given him.

"I am ready to appear before a tribunal (Cambodian or international) responsible for judging the Khmer Rouge and their real or supposed accomplices," the constitutional monarch said in a statement from his residence in Beijing.

King Sihanouk briefly served as head of state during the Khmer Rouge's bloody revolutionary regime in the 1970s.

The announcement came one day after the Cambodian government permitted two Khmer Rouge leaders to return to a remote part of the country still under nominal control of the former ruling political group, dimming the chances that the two would stand trial for genocide.

Samphan departs for a tour of Cambodia

Top government officials denied they were allowing Khieu Samphan and Nuon Chea to escape justice. Yet the government surprised Cambodians and international rights activists when it warmly received them last week rather than forcibly detaining them.

Samphan and Chea defected to the government amid calls that they face an international tribunal for genocide and crimes against humanity. The two were key leaders in the late Pol Pot's bloody revolution in Cambodia between 1975 and 1979. An estimated 1.7 million lives were lost during Pol Pot's rule.

The government insisted it favors a trial, but could not detain the men because there was no warrant for their arrest, a spokesman said.

"Everyone is presumed innocent until they are proven guilty," government spokesman Khieu Kanharith said.

"We say they are free to go until they are summoned by a court," he said. "If the court does summon them and they don't return, then they can be in contempt of court. ... How can you be sure they won't return?"

Evidence of a violent past at the Chaung Ek torture camp in Phnom Penh

The two flew in a military helicopter from the northwestern town of Battambang to the western town of Pailin near the Thai border in the morning, Battambang police chief Chan Kosal said.

The government has argued that arresting them in Phon Penh could spark a civil strife in Cambodia. But it could face serious hurdles in apprehending the Khmer Rouge leaders in Pailin should arrest warrants be issued, many analysts say.

The government nominally controls Pailin, near the Thai border some 300 km (185 miles) northwest of Phnom Penh. But Ieng Sary, another top Khmer Rouge leader who received a royal amnesty after his 1996 defection, effectively controls the region.

Lao Mong Hay, director of the Khmer Institute of Democracy, criticized the government for not arresting the two.

"They shouldn't have allowed them to go back," he said. "They should have arrested and detained them while waiting for the United Nations to decide on a tribunal."

The United Nations has hired experts to study the establishment of a court to put Khmer Rouge leaders on trial. They are expected to make a report at the end of January.

Prime Minister Hun Sen said on Friday he backed a trial but the courts should decide when and how to initiate court proceedings. While saying he could not give anyone immunity, he stressed his first priority was national reconciliation.

The prime minister received heavy criticism when he suggested last week that a trial might not be in the national interest.

"Hun Sen says it's not up to him, but from a legal point of view he's completely wrong," said political analyst Raoul Jennar, who runs the Center for Cambodian Research.

"The prosecution is the responsibility of the society, and the executive has the power to order the prosecution. He has the power to act, but doesn't want to. He wants to turn the page," he said.

Lao Mong Hay said the two should have been held under a law outlawing the Khmer Rouge pending further warrants.

He believed the reason the government had not been willing to take legal action was pressure from countries like Vietnam, China and Thailand, all of which have been closely involved with the Khmer Rouge in the past.

Hun Sen said Friday that Thailand had handed over the two men on the condition that they be allowed to "return to live in society."

The government also might be concerned about the extent of any genocide investigation, Lao Mong Hay said. Government figures, including Hun Sen, were once members of the Khmer Rouge.

An Asian diplomat termed the decision to let the two go back "honor among thieves," while Lao Mong Hay said:

"They are playing a dangerous cat-and-mouse game. Now they can always try to say they can't get them back."

He and Jennar said there was a real danger now that with three top Khmer Rouge leaders back together in Pailin, what had been an essentially defeated movement could have the opportunity to rebuild and regroup its remaining forces.

On Wednesday, King Sihanouk said he would not give the defectors immunity as he had for Ieng Sary, and that an international tribunal would have a perfect right to try them.

His son, Prince Norodom Ranariddh, president of the National Assembly and leader of the royalist party that is the junior partner in a fragile ruling coalition, said the two should be tried in Cambodia, but preferably with outside help.

Reuters contributed to this report.