Philippines President Rodrigo Duterte launches tirade against Barack Obama

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 crime war 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 the 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 on the sidelines of a summit of global leaders hosted by the Association of Southeast Asian Nations (ASEAN) in Vientiane, the Lao capital.

Responding to Philippine leader's foul-mouthed tirade, Obama on Monday cast doubt on his planned meeting with Duterte.

"He's a colourful guy," Obama joked on the eve of the scheduled face-to-face, before pointedly noting: "I always want to make sure if I'm having a meeting that it's actually productive."

Duterte was elected in May after a promise to wage an unprecedented war on illegal drugs that would see tens of thousands of suspects killed.

Official figures released on Sunday show that, since Duterte took office on June 30, over 2,400 people have been killed in police anti-drug operations and by suspected vigilantes.

Duterte has angrily rejected criticism from the Catholic Church, human rights groups, legislators and the United Nations.

Duterte vowed Monday the bloodbath would continue as he pursued his goal of eradicating illegal drugs in the Philippines.

"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.

Duterte insisted he would not take orders from the United States, a former colonial ruler of the Philippines, and did not care about how he was perceived.

"I don't give a shit about anybody observing my behaviour," he said.

Duterte also used vulgar language to accuse his domestic critics of wanting to please the United States.

"There are others who have the mental capacity of dogs who lap at the ass of the Americans," he said in reference to his critics.