"Let me tell you about human rights," the diplomat quoted Duterte as saying while displaying a picture of Filipinos killed by American soldiers about a century ago.
"This is my ancestors being killed, so why now we are talking about human rights? We have to talk of the full spectrum of human rights."
Duterte launched into a tirade about US military killings in the Philippines when it was an American colony from 1898 to 1946, according to three diplomats that Agence France-Presse spoke with who were in the room.
"The Philippine president showed a picture of the killings of American soldiers in the past and the president said: 'This is my ancestor they killed. Why now we are talking about human rights," an Indonesian delegate said.
The delegate described the atmosphere in the room as "quiet and shocked."
Another diplomat described the speech as "normal Duterte."
Duterte spoke after Obama had delivered a speech that referred to human rights.