Two senior Khmer Rouge leaders have returned to their jungle stronghold, reducing their chances of their standing trial for genocide.

Khiu Smphan and Nuon Chea were flown to a Khmer-run area in a Cambodian army helicopter on Sunday.

The government says it had no choice because no arrest warrants existed for the two men.

Cambodian Prime Minister, Hun Sen, aroused international condemnation by treating Khiu and Nuon as VIPs. Since turning themselves over to the Camboadian government they have been on a whirlwind tour of the country.

Hun Sen said he would not arrest them for genocide, hinting that such an arrest could ignite Cambodia's bloody twenty-year civil war. He later changed his mind and said "the genocidal regime of Pol Pot must be punished."

King Norodom Sihanouk said he would not sign amnesty agreements for the Khmer leaders.

Khiu and Nuon are widely thought to be principal architects of the disastrous reign of the Khmer Rouge in the 1970s, during which nearly two million people were killed.

The Khmer Rouge was ousted by a Vietnamese invasion in 1979, fighting a guerrilla war until the mid-1990s. In recent months, a combination of defections and military defeats has reduced the once-powerful movement to small bands of poorly-armed soldiers.

The former Khmer Rouge leader, Pol Pot, died in 1998.