Yesterday, the White House said Trump had invited Duterte in a "friendly" call in which the leaders discussed the Filipino president's fight against drugs and the two countries' alliance.
The statement touched only lightly on Duterte's brutal crackdown on crime, which has claimed thousands of lives and drawn international condemnation.
But when White House chief of staff Reince Priebus was asked today why Trump was "honouring" Duterte with the White House invitation, he told ABC, "I'm not so sure it's a matter of honouring this president."
That way, Priebus added, "if something does happen in North Korea, we have everyone in line backing up a plan of action that may need to be put together with our partners in the area".
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Duterte had in the past regularly hit out at the United States, Philippines' one-time colonial ruler, for perceived hypocrisy over human rights. Last year, he branded then US president Barack Obama a "son of a whore" for criticising the drug war.
But the White House said yesterday that the two leaders, both elected to office last year, had helped orient the US- Philippine relationship "in a very positive direction".
The White House said Trump "enjoyed the conversation" with Duterte, and looked forward to attending the key US-ASEAN and East Asia summits in the Philippines in November.
Duterte's spokesman Ernesto Abella confirmed Trump's invitation, although he gave no indication of when the visit would take place.
Philippines police have reported killing 2,724 people as part of the anti-drug campaign, although authorities insist the shootings have been in self-defense.
Many thousands of others have been killed by shadowy vigilantes, according to rights groups.
A Philippine lawyer last week filed a complaint at the International Criminal Court accusing Duterte of mass murder, alleging his war on drugs had led to about 8,000 deaths.
When Priebus was asked whether Trump had raised that record with Duterte, he said he had not personally sat in on the entire phone call. But the purpose of the call, he added, was "all about North Korea".
In the Philippines, Duterte's pledge to stop the country turning into a narco-state has proved wildly popular with millions of Filipinos looking for a quick solution to crime and corruption.
Duterte is the latest in a series of authoritarian leaders with whom Trump has established friendly relations, including Egypt's Abdel Fattah al-Sisi and Turkish President Recep Tayyip Erdogan. And he often spoke warmly of President Vladimir Putin of Russia -- until differences over Syria erupted.