US President Barack Obama has cancelled what would have been his first meeting with Rodrigo Duterte, according to a White House spokesman, hours after the Philippine leader described his American counterpart in vulgar terms.
Duterte called Obama a "son of a whore", saying that he would not be lectured by the US leader on human rights, according to AFP news agency.
Duterte's tirade came as he bristled at warnings he would face questioning by the US president at their scheduled meeting over his war against drugs in the Philippines, which 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 on Monday.
"We will be wallowing in the mud like pigs if you do that to me," he said.
However, a statement released by the Philippine president on Tuesday expressed regret for the tirade against his US counterpart.
"While the immediate cause was my strong comments to certain press questions that elicited concern and distress, we also regret it came across as a personal attack on the US president," the statement said.
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 capital of the Laos.
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Shortly after Duterte's comments, Obama had appeared to cast doubt on whether a meeting could take place with the Philippines president. Calling Duterte "a colourful guy", Obama said he was asking his staff to find out whether a meeting would be useful.
"I always want to make sure if I'm having a meeting that it's actually productive and we're getting something done," he told reporters.
Duterte, 71, was elected in May after promising to wage an unprecedented war on drugs.
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Official figures released on Sunday showed that, since Duterte took office on June 30, more than 2,400 people have been killed in police anti-drug operations and by suspected vigilantes.
Speaking on the sidelines of the G20 summit in the Chinese city of Hangzhou, Obama said Washington recognised that drugs were a significant problem for the Philippines.
But he also insisted that he would not shy away from raising concerns about the way the issue was being handled under the new administration.
"The issue of how we approach fighting crime and drug trafficking is a serious one for all of us. We've got to do it the right way," Obama said.
"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."
'More people will be killed'
Duterte has previously angrily rejected criticism from the Catholic Church, human rights groups, politicians and the United Nations.
"More people will be killed, plenty will be killed until the last pusher is out of the streets. Until the [last] drug manufacturer is killed, we will continue and I will continue," he said on Monday.
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Duterte insisted he would not take orders from the US, a former colonial ruler of the Philippines, and did not care about how he was perceived.
The maverick president has quickly earned a reputation for making offensive comments about his critics.