President Obama is a "son of a bitch," Philippines president Rodrigo Duterte said Monday.

Duterte said he would swear at Obama at a scheduled meeting if the president raises the issue extrajudicial killings of drug suspects in the Philippines.

Around 2,400 suspected drug dealers and users have been killed without trial, in a drug war Duterte launched after taking office in June. His efforts have won public support, but the killings have concerned Washington and United Nations officials.

Obama is scheduled to meet with Duterte in Laos at the summit of the Association of Southeast Asian Nations, but hinted Monday he might cancel the meeting. Obama said the lack of due process in Duterte's anti-drug campaign is "something that's going to be brought up" if the two meet.

When asked about meeting with Obama, Duterte said "son of a bitch, I will swear at you," if he brought up the issue.

"I am a president of a sovereign state and we have long ceased to be a colony. I do not have any master except the Filipino people, nobody but nobody. You must be respectful. Do not just throw questions. Putang ina I will swear at you in that forum," he said, using the Tagalog phrase for son of a b——.

Obama said he has directed aides to investigate whether a meeting with Duterte can still be productive. He said Duterte is a "colorful guy," when asked whether he had heard the threat. Duterte has previously cursed the pope and U.N. Secretary-General Ban Ki-moon.