Obituaries: Ieng Sary: right-hand man of Pol Pot

Ieng Sary, who has died aged 87, was a former Khmer Rouge official whose defection from the Cambodian Maoist rebel group in 1996 led to its collapse, bringing an end to nearly two decades of conflict.

The Khmer Rouge ruled Cambodia from 1975 to 1979 and aimed to transform the country into a pure socialist society. To this end they abolished money, private property, religion and traditional culture. Cities were emptied, forcing urban residents to become rural labourers, growing rice and building irrigation schemes.

In four years, between 1.7million and 2.2million people - a quarter of the population - died in the "killing fields" from starvation, disease, overwork, torture and mass execution.

Ieng Sary and his wife, Ieng Thirith, were members of Khmer Rouge leader Pol Pot's inner circle. Ieng Sary served as deputy prime minister in charge of foreign affairs until 1979, when Vietnamese forces ousted the Khmer Rouge; a new Hanoi-installed government sentenced the two men to death in absentia.

The Khmer Rouge retreated to the Thai border, where they continued fighting for nearly two more decades. During these years Ieng Sary was a crucial link between the organisation and China, a key source of money and arms. Former colleagues later accused him of embezzling millions of dollars from illegal logging and gem-mining operations along the border with Thailand.

In 1996, however, with the group's fortunes on the wane, Ieng Sary struck a peace deal and led 3000 Khmer Rouge fighters out of the jungle. The move was a catalyst for the movement's final disintegration in 1999 and secured Ieng Sary a royal pardon, a measure of credibility as a peacemaker and a comfortable life, which he divided between an opulent villa in Phnom Penh and another home in Pailin, northwestern Cambodia.

Ieng Sary claimed that Pol Pot had been "the sole and supreme architect of the party's line, strategy and tactics" and that he had been only a secondary figure, excluded from decisions on policy and executions. "Do I have remorse? No," he said in 1996. "This was not my responsibility."

But campaigners fighting for justice soon found evidence that Ieng Sary had been deeply involved in the bloody purges.

In 2007, Ieng Sary was arrested by a joint Cambodian-UN tribunal and put on trial for genocide, crimes against humanity and breaches of the Geneva Convention. But he died before any verdict could be reached.

The Khmer Rouge almost destroyed Cambodian Buddhism, yet towards the end of his life Ieng Sary claimed to be a believer. "I am a gentle person. I believe in good deeds," he claimed.