Former Khmer Rouge foreign minister Ieng Sary and his wife Ieng Thirith have been arrested.
This brings to four the number of regime leaders now facing Cambodia's UN-backed genocide court.
The elderly couple, who were seized at their villa in the capital Phnom Penh, will face charges of crimes against humanity.
Ieng Sary will face additional war crimes charges.
Ieng Sary was the public face of the Khmer Rouge while his wife became the regime's social affairs minister.
Up to two million people died of starvation and overwork, or were executed, under the Khmer Rouge's rule over Cambodia from 1975 to 1979.
Regime leader Pol Pot died in 1998, but his deputy Nuon Chea and Duch, who oversaw the notorious Tuol Sleng torture centre, were arrested by the tribunal earlier this year.
The court got under way last year after a decade of tense negotiations between the UN and Cambodian government.
Trials are expected in 2008 amid concern that some of the ageing defendants could die before ever seeing the inside of a courtroom.
