VIENTIANE, LAOS-President Barack Obama threatened Monday to call off a planned meeting with new Philippine President Rodrigo Duterte, seeking distance from a USA ally's leader during a diplomatic tour that's put Obama in close quarters with a cast of contentious world figures.

The leaders are in Laos for the the Association of Southeast Asian Nations (ASEAN) and East Asia summits, but the frank public exchanges threaten to overshadow the event.

US President Barack Obama boards Air Force One prior to departure from Hangzhou Xioshan International Airport in Hangzhou on September 5, 2016, following the conclusion of the G20 Summit.

White House officials previously said Obama would confront the Philippines President about his country's handling of drug dealers, including extra-judicial killings, or government executions without the benefit of judicial proceedings or due process.

Mr Duterte said if he did that, "Putang ina (son of a whore) I will swear at you in that forum".

The Bagong Alyansang Makabayan said the cancellation was "not a big loss" and lauded Duterte's broadside at Obama as "the first time in forever" a Philippine president "has the backbone to reject United States intervention".

President Obama has indicated he may call off a scheduled meeting with President Rodrigo Duterte of the Philippines after the notoriously foul-mouthed Filipino threatened to "swear" at his American counterpart should he question a violent government crackdown on alleged criminals.

Bayan said the cancelled meeting would have been used by the United States to "to feign concern for human rights and then arm-twist the Philippines regarding the USA imperialist agenda in the country and the West PH Sea".

The White House said Mr Obama cancelled the talks in response to the "vulgar" comments, and will instead meet with South Korean President Park Geun-hye. Aides said Obama's visit will probably echo a stop in Hanoi, Vietnam, in May, when the president declared he was "mindful of the past, mindful of our hard history, but focused on the future". Do not just throw away questions and statements.

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"He's a colorful 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 would be actually productive". He called Pope Francis a "son of a whore" in May, and called US Ambassador Philip Goldberg a "gay son of a whore".

Obama noted that, while the fight against drugs was tough, the U.S. would always assert the need for due process and to carry out the campaign in a way that is consistent with basic worldwide norms.

He made it clear, "I do not want to pick a quarrel with Obama, but certainly I would not want to be beholden to anybody.I am only accountable to the Filipino people who elected me".

He said he would ask Indonesian President Joko Widodo for mercy for Mary Jane Veloso, who is in Indonesia's death row after being convicted of being a drug courier.

Mr Duterte added he did not believe the "rude" subject of extrajudicial killings should be raised at such a summit. Many will die, 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'.

Mr. Duterte will also officially receive from Sisoulith the chairmanship of the Asean meeting which will be held in the Philippines next year.

With a reputation as a tough-on-crime former mayor, Mr Duterte has alarmed human rights groups with his deadly campaign against drugs, which Mr Duterte has described as a harsh war.