United States President Barack Obama has cancelled his planned meeting with the divisive President of the Philippines after he lashed out at the US President, calling him a "son of a bitch".
Rodrigo Duterte was due to meet President Barack Obama at a regional summit in Laos.
He warned the American leader to think twice about raising the issue of illegal killings.
"Who does he think he is? I am no American puppet. I am the president of a sovereign country and I am not answerable to anyone except the Filipino people," Duterte said in a scornful speech on Monday (local time). "Son of a bitch, I will swear at you."
He says the Philippines inherited the drug problem from the United States. "Why? Because they invaded this country and made us their subjugated people. Everybody has a terrible record of extra-judicial killing. Why make an issue about fighting crime?"
Duterte had said earlier that "plenty will be killed" before the end of his campaign against illegal drugs that has led to the death of about 2400 people since he became president two months ago.
"What I've instructed my team to do is to talk to their Philippine counterparts to find out, is this in fact a time where we can have some constructive, productive conversations," Obama said at a news conference at the end of a G20 summit in the eastern Chinese city of Hangzhou.
"Obviously the Filipino people are some of our closest friends and allies and the Philippines is a treaty ally of ours. But I always want to make sure that if I'm having a meeting that it's actually productive and we're getting something done."
Obama noted that, while the fight against drugs was tough, the US would always assert the need for due process and to carry out the campaign in a way that is consistent with basic international norms.
"And so, undoubtedly, if and when we have a meeting, this is something that's going to be brought up, and my expectation, my hope is that it could be dealt with constructively.
"But I'll have my team discuss this... I want to make sure that the setting is right and the timing is right for us to have the best conversation possible."