Cambodia's Killing Fields court charged former Khmer Rouge Foreign Minister Ieng Sary and his wife on Monday with crimes against humanity, the latest members of Pol Pot's inner circle to face justice.

The octogenarian Ieng Sary, who became the international face of the Beijing-backed ultra-Maoist revolution after it was overthrown by a 1979 Vietnamese invasion, also stands accused of war crimes, a court spokesman said.

Ieng Sary and Khieu Thirith -- sister of Pol Pot's first wife, Khieu Ponnary -- were arrested soon after dawn by rifle-toting police who sealed off the Phnom Penh villa where they have lived since cutting a deal and surrendering in 1996.

They were then whisked away in a police convoy to the court compound on the western outskirts of the capital to face the Cambodian and international judges probing their alleged role in one of the 20th century's darkest chapters.

An estimated 1.7 million people were executed or died of torture, disease or starvation under the Khmer Rouge's four-year reign of terror between 1975 and 1979.

Ieng Sary has denied having anything to do with the mass killings 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 U.N.-backed 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, Khieu Thirith and Khieu Ponnary, went on to become the Khmer Rouge's highest ranking officers. Khieu Ponnary died in 2003 after a long mental illness.

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

(Reporting by Ek Madra; Writing by Ed Cropley, editing by Michael Battye and Sanjeev Miglani)