His lawyers said he was hospitalized with gastrointestinal problems on March 4. Mr. Ieng Sary had been treated for heart problems and other ailments for years. His death was announced by the special tribunal trying him, with United Nations backing.
Mr. Ieng Sary, a brother-in-law of Pol Pot, the top leader of the Khmer Rouge, was part of an inner circle of Paris-educated communists who led the movement, which caused the deaths of 1.7 million people from starvation, overwork and execution during its rule over Cambodia from 1975 to 1979.
Only one person, Kaing Guek Eav, a prison commander known as Duch, has been convicted in connection with those deaths. He was sentenced to life in prison in February 2012. The remaining defendants are Nuon Chea, the movement’s chief ideologue, and Khieu Samphan, the nominal head of state of the Khmer Rouge. Both are in their 80s.
As foreign minister, Mr. Ieng Sary helped persuade hundreds of Cambodian diplomats and intellectuals to return home from overseas to help the new revolutionary government. The returnees were sent to “re-education camps,” and most were executed.
Mr. Ieng Sary “repeatedly and publicly encouraged, and also facilitated, arrests and executions within his Foreign Ministry and throughout Cambodia,” wrote Steve Heder, a Cambodia scholar who assisted the tribunal and is co-author of “Seven Candidates for Prosecution: Accountability for the Crimes of the Khmer Rouge.”
“I have done nothing wrong,” Mr. Ieng Sary said before his arrest in 2007. “I am a gentle person. I believe in good deeds. I even performed good deeds to save several people’s lives.”
At a news conference, he blamed Pol Pot for the mass killings and also pointed a finger at Nuon Chea, who he said was implicated in torture and execution.
The tribunal, formally the Extraordinary Chambers in the Courts of Cambodia, expressed regret over Mr. Ieng Sary’s death. The defendants have all been in and out of the hospital since their arrests, and the tribunal has tried to assure that they survive to hear their sentences.
“The death of Ieng Sary is another blow to the Extraordinary Chambers and is an example of ‘justice delayed is justice denied,’ ” said Long Panhavuth, who has been following the trial closely as program coordinator of the Cambodia Justice Initiative, an indepedent monitoring program. “It is unfortunate that the trial chamber could not complete the judgment while the accused and the victims are still alive.”
Mr. Ieng Sary’s wife, Ieng Thirith, whose sister was married to Pol Pot, was also a defendant until she was excused because she has dementia.
Pol Pot himself died in 1998 in a jungle stronghold of the Khmer Rouge and never faced a courtroom.
Mr. Ieng Sary was deputy prime minister for foreign affairs and a permanent member of the Communist Party of Kampuchea’s Standing Committee during the Khmer Rouge’s rule over Cambodia, which it then called Democratic Kampuchea.
During the trial, Mr. Ieng Sary’s lawyers argued that he was protected by a pardon in 1996 by the late King Norodom Sihanouk absolving him of a conviction in absentia for genocide in a show trial in 1979, shortly after the Khmer Rouge were driven from power by a Vietnamese invasion. The court, however, ruled that the amnesty did not apply in this case.
After the Khmer Rouge was ousted, Mr. Ieng Sary continued a civil war against the new government until he surrendered with thousands of troops in 1996 in return for the king’s pardon. Until his arrest he had lived openly in a villa in Phnom Penh, traveling often to Thailand for medical treatment.
Mr. Ieng Sary was born on Oct. 24, 1925, in Tra Ninh province in Southern Vietnam to an ethnic Cambodian father and an ethnic Chinese mother. His birth name was Kim Trang, and he later used the revolutionary name Van.
He was one of a group of future Khmer Rouge leaders, including Pol Pot, who received scholarships to study in France, where he became a member of the French Communist Party in 1951.
After returning to Phnom Penh in 1957 he taught history in high school and became an underground member of the Communist Party of Cambodia. He fled to the jungle in 1963 when suspected communists were being arrested.
In 1970, as the Khmer Rouge gained momentum and as war raged in neighboring Vietnam, he went to Hanoi to establish a radio station for his revolutionary movement. He then flew to Beijing, where he was given a permanent base in 1971, according to testimony in the trial.
He returned permanently to Cambodia in April 1975, a moment known as “Year Zero,” when the Khmer Rouge marched into Phnom Penh and began transforming the country.