Former Khmer Rouge prison commander Kaing Guek Eav, also known as Duch, sits in the courtroom at the UN-backed tribunal on March 30, 2009 in Phnom Penh, Cambodia. (Mak Remissa/Pool/Associated Press)

A former Khmer Rouge commander testified Monday that he was responsible for the brutal deaths of babies under an official policy aimed at ensuring children of the Cambodian regime's adult victims could never avenge their parents' deaths.

"I am criminally responsible for killing babies, young children and teenagers," Kaing Guek Eav, known as Duch, told a UN-assisted genocide tribunal in Phnom Penh.

"It was done by my subordinates. I do not blame them because this was under my responsibility."

Duch, 66, is being tried for crimes against humanity, war crimes, murder and torture. He was the commander at the Khmer Rouge's notorious S-21 prison in Phnom Penh.

"There is no gain to keep them [children] and they might take revenge on you," Duch said, reciting the policy that he said he learned from the regime's former defence minister, Son Sen.

An estimated 16,000 men, women and children are thought to have been tortured at the prison before being executed. It's not known how many young children were killed at S-21 because few records were kept of them. But prison officials took meticulous records of the adults who were imprisoned and killed there.

Last year, Duch was taken to the former prison, now converted into a museum, and shown drawings of Khmer Rouge guards swinging babies by their legs and pounding their heads against tree trunks.

"The horrendous images of the babies being smashed against the trees, I didn't recognize it at first," said Duch. But after seeing photographs of some of the children, he recalled such things had happened, though he did not mention whether he carried out such killings himself.

About 1.7 million Cambodians died under the 1975-79 communist Khmer Rouge regime from forced labour, starvation, medical neglect and executions.

Duch is the first senior member of the regime to stand trial, and the only one to acknowledge responsibility for his actions. Other senior leaders who have been detained are Khieu Samphan, Nuon Chea, Ieng Sary and Ieng Sary's wife, Ieng Thirith. They are likely to face trial in the next year or two.

With files from The Associated Press