PHNOM PENH, Cambodia — The deputy leader of the Khmer Rouge regime blamed for 1.7 million deaths in Cambodia’s “killing fields” insisted Tuesday that he carried out its policies for the sake of Cambodians and to protect the country from invaders.

The communist movement’s chief ideologist did not directly respond to the horrors that prosecutors described a day earlier at the start of the U.N.-backed tribunal for him and two other top Khmer Rouge leaders.

Instead, Nuon Chea gave a political history of the movement and Cambodia, insisted his role was patriotic, and blamed neighboring Vietnam for much of the country’s troubles.

“I had to leave my family behind to liberate my motherland from colonialism and aggression and oppression by the thieves who wish to steal our land and wipe Cambodia off the face of the Earth,” Nuon Chea said in his first public comments at the trial. “We wanted to free Cambodia from being a servant of other countries, and we wanted to build Cambodia as a society that is clean and independent, without any killing of people or genocide.”

The tribunal is seeking justice on behalf of the 1.7 million people – as much as a quarter of Cambodia’s then-population – estimated to have died from executions, starvation, disease and overwork when the Khmer Rouge held power from 1975 to 1979.

The three most senior surviving leaders – Nuon Chea, 85, former head of state Khieu Samphan, 80, and former Foreign Minister Ieng Sary, 86 – are charged with crimes against humanity, genocide, religious persecution, homicide and torture. They have long denied blame.

Nuon Chea was the Khmer Rouge’s second-highest leader after Pol Pot, who died in 1998 in a jungle while a prisoner of his own comrades.

Earlier Tuesday, prosecutors said the defendants cannot blame Pol Pot alone for the atrocities that took place.