A day ahead of their planned meeting in Laos for the regional summit of the Association of Southeast Asian Nations (ASEAN), new Philippine President Rodrigo Duterte described Obama as a "son of a whore" to reporters.

Obama learned of the remark on the last day of the G20 summit in Hangzhou, China. He said he had told his aides to speak with officials in the Philippines "to find out is this, in fact, a time where we can have some constructive, productive conversations."

"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 told reporters.

Obama will instead meet with South Korean President Park Geun-hye, said Ned Price, spokesman for the White House National Security Council.

Abusive history

The Philippine president later expressed regret in a statement issued in the Laotian capital, Vientiane.

"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," he said in a statement. He added that he was looking forward to meeting Obama at a later date and "ironing out differences" between the two countries.

It's not the first time that Duterte has caused insult with vulgar language. Earlier this year, he reportedly called Pope Francis a "son of a whore" and US Ambassador Philip Goldberg was described as a "gay son of a whore."

Duterte's ire appears to have been raised after it was made known that Obama would discuss human rights during the planned meeting. The Philippine president said this would be "rude."

Rights groups have raised concerns over the reported deaths of more than 2,400 people in the crackdown on illegal drugs in the Philippines. Ahead of the planned meeting, Obama said he was aware of the importance of fighting the drug trade but said it must be done under the rule of law.

Duterte responded by saying: "Plenty will be killed until the last pusher is out of the streets. Until the [last] drug manufacturer is killed we will continue."

Key ally in South China Sea dispute

The Philippines has been a key US ally in its dispute with China over freedom of movement in the South China Sea. In July, an arbitration court in The Hague invalidated China's territorial claims to most of the sea after a case was brought by the Philippines.

The US has accused China of militarizing a global trade route and bringing freedom of movement at sea and in the air into jeopardy.

Brunei, Malaysia, the Philippines, Taiwan and Vietnam have rival territorial claims to the sea.

The ASEAN summit is being held in Vientiane, in Laos. The 10 members of the bloc, Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand and Vietnam, will also meet with the leaders of China, Japan, South Korea, Australia, India, Russia and the United States.

jm/cmk (Reuters, AP)