Police and security guards from Cambodia's "Killing Fields" tribunal arrested former Khmer Rouge Foreign Minister Ieng Sary on Monday, the third Pol Pot henchman to be taken into custody by the U.N.-backed court.

The octogenarian, who became the international face of the Beijing-backed ultra-Maoist revolution after it was overthrown by a 1979 Vietnamese invasion, will be charged with crimes against humanity and war crimes, a tribunal statement said.

His wife, Khieu Thirith, another member of Pol Pot's inner circle and the sister of Pol Pot's first wife, Khieu Ponnary, was also arrested to face charges of crimes against humanity. Khieu Ponnary died in 2003 after a long mental illness.

Ieng Sary and Khieu Thirith, who had lived in a luxury Phnom Penh villa since cutting a deal and surrendering to the government in 1996, were detained soon after dawn, then whisked away in a police convoy with sirens blazing.

An estimated 1.7 million people were executed or died of torture, disease or starvation under the Khmer Rouge between 1975 and 1979.

Ieng Sary has denied having anything to do with the atrocities but spent much of the 1980s defending Pol Pot at the United Nations while remnants of his black-shirted guerrilla army continued to fight from the jungle.

He and Khieu Thirith are the third and fourth senior cadres to be arrested since the $56 million tribunal got off the ground in earnest this year after almost a decade of delays.

Duch, who ran the "S-21" interrogation and torture centre at Phnom Penh's former Tuol Sleng high school, has been charged with crimes against humanity, as has "Brother Number Two" Nuon Chea, who is also accused of war crimes.

While Nuon Chea has proclaimed his innocence, Duch, in interviews with Western reporters, has confessed to his role in the mass killings and is expected to be a key witness against other senior regime figures.

"Brother Number One" Pol Pot died in 1998 in the final Khmer Rouge redoubt of Anlong Veng, a jungle-clad mountain on the border with Thailand.

Ieng Sary was born in 1924 as Kim Trang but, like many Cambodians, had a penchant for aliases, including Van, Thang and Nenn.

He was a member of a group of young Cambodians imbued with socialist and communist zeal while studying on government scholarships in Paris in the 1950s.

Many members of the group, which also included Pol Pot, former President Khieu Samphan and Khieu Thirith, went on to become the Khmer Rouge's highest ranking officers.

Reports of his ill-health have been frequent in the past few years, including some suggestions he has traveled to Bangkok for heart treatment.

 PHOTO CAPTION

Some of the 8000 skulls of victims of the Khmer Rouge are seen on display at the Cheoung Ek "Killing Fields" memorial, 11 miles on the outskirts of the Cambodian capital Phnom Penh.