Philippine President Rodrigo Duterte called Barack Obama a "son of a whore" on Monday as he vowed not to be lectured by the US leader on human rights when they meet in Laos.
The acid-tongued Duterte bristled at warnings he would face questioning by the US president over a war against drugs in the Philippines that has claimed more than 2,400 lives in just over two months.
"You must be respectful. Do not just throw away questions and statements. Son of a whore, I will curse you in that forum," Duterte told a news conference shortly before flying to Laos to attend a summit.
"We will be wallowing in the mud like pigs if you do that to me."
Duterte was due to hold a bilateral meeting with Obama on Tuesday afternoon on the sidelines of a gathering of global leaders hosted by the Association of Southeast Asian Nations (ASEAN) in Vientiane, the Lao capital.
But shortly after Duterte spoke, Obama appeared to cast doubt on whether such a meeting could take place.
Calling Duterte "a colourful guy", the US president said was asking his staff to find out whether a meeting would be useful.