Philippine President Rodrigo Duterte expressed regret on Tuesday that a tirade against Barack Obama, in which he called the US leader a "son of a whore", came across as a personal attack.

Longtime allies the United States and the Philippines have seen relations plunge under a barrage of insults from Duterte since he came to office on June 30.

The latest Duterte outburst came on Monday before a planned meeting between the leaders at a regional summit in Laos.

Obama responded to the outburst by cancelling the talks, which prompted a Duterte to offer a qualified expression of regret. 

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," a statement released by Duterte said.

The 71-year-old former prosecutor was referring to his remarks on Monday, when he warned he would not be lectured by Obama over concerns about a brutal war on drug crime that has claimed more than 2,400 lives in the Philippines.

"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 reporters when asked about his message for Obama.

Duterte, who has quickly earned a global reputation for his jibes, then used typically colourful language to describe their planned meeting if rights issues came up.

"We will be wallowing in the mud like pigs if you do that to me," he said.

Duterte's about-turn on Tuesday said both sides would hold face-to-face talks "at a later date".

"Our primary intention is to chart an independent foreign policy while promoting closer ties with all nations especially the US with which we have a longstanding partnership," Duterte's statement said.

The Philippines' Department of Foreign Affairs added Duterte had "a deep regard and affinity for President Obama and for the enduring partnership between our nations".

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

During his Monday outburst he said the bloodbath would continue.

"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.

He also added 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.

Source: AFP