The president is scheduled to attend a pair of worldwide summits and meet several times with Philippine President Rodrigo Duterte.
"He is not the Human Rights Commission". Trump has previously praised Duterte's handling of his nation's drug problems.
The leader of the Philippines has come under intense criticism from human rights advocates for overseeing a violent drug crackdown that includes extrajudicial killings. Worldwide organizations, including the United Nations, have accused him of subverting justice and indiscriminate killing.
It is not the first time the Philippines leader has claimed to have killed someone. "I don't care about human rights, believe me".
But Trump and Duterte have expressed mutual admiration for other.
"What makes the death of people in the Philippines more important than the rest of the children in the world that were massacred and killed?"
Duterte has also repeatedly bragged about personally killing people when he was younger. "Jeez. When I was a teenager, I was in and out of jail". A person, really. During a fight. "Stabbing. That was when I was 16 years old, just because we just looked at each other", he said.
Duterte's spokesman, Harry Roque, has since told the British news network that the comment was made in jest.
Trump is in Hanoi for a brisk visit that could touch on boosting military support for America's former wartime foe.
Ahead of his trip to Vietnam, Duterte said he would ask his Chinese counterpart what Beijing's intentions in the region are. He was slated to stay in the Philippines for two days but the POTUS announced that he will stay for another for the East Asia Summit.
Trump is expected to arrive in Manila this weekend for the 31st Association of Southeast Asian Nations (ASEAN) Summit and related meetings.
Speaking to an audience of Filipinos in Vietnam, Mr Duterte said he told Ms Callamard: "If you investigate me, I will slap you".
A Trump administration official, in previewing the visit, stressed that Trump and Duterte have "a warm rapport".
Trump headed to Manila later yesterday for the final stop on his marathon Asia tour that has mainly focused on building regional consensus against North Korea's nuclear ambitions and espousing his "America First" vision of global trade.
In a letter to Trump, members of the Tom Lantos Human Rights Commission on Capitol Hill urged Trump to address the extrajudicial killings.