VIENTIANE: Philippine President Rodrigo Duterte expressed regret Tuesday over his "son of a bitch" remark while referring to US President Barack Obama, in a rare display of contrition by a politician whose wide arc of profanities has unabashedly targeted world figures including the pope and the UN chief.

In a statement read out by his spokesman, Duterte said that while his "strong comments" in response to certain questions by a reporter "elicited concern and distress, we also regret it came across as a personal attack on the US president."

Duterte had made the untampered remarks Monday before flying to Laos, where he is attending a regional summit. He had been scheduled to meet Obama separately, but Obama indicated he had second thoughts.

On Tuesday, Duterte said both sides mutually agreed to postpone the meeting.

Even though Duterte's latest comment does not amount to an apology, the expression of regret is unusual for the tough-talking former mayor, who is unapologetic about his manner of speech and liberally peppers his casual statements with profanities such as "son of a bitch" and "son of a whore."

But perhaps Duterte's aides realised it would be unwise to take on the most powerful official in the world, and there would be a price to pay for insulting the president of the United States.

The US is one of the Philippines' largest trading partners and a key security ally in its fight against terrorism in the country's south. Manila also needs Washington's help in dealing with a more assertive China in the disputed South China Sea.

Duterte likely had realised his folly by the time he arrived in the Laotian capital of Vientiane on Monday night.

Speaking to reporters here, he said, "I do not want to quarrel with the most powerful country on the planet," but immediately took his typical combative approach by saying: "Washington has been so liberal about criticising human rights, human rights and human rights. How about you? I have so many questions also about human rights to ask you. So ... people who live in glass houses should not" throw stones at others.

He said if the White House had problems with him, it could have sent him a diplomatic note and let him respond. "There's a protocol for that," Duterte said. "You just cannot shoot a statement against the president of any country."

But by Tuesday, he had done a complete U-turn in the tone of his statement.

"We look forward to ironing out differences arising out of national priorities and perceptions, and working in mutually responsible ways for both countries," the statement said.

The flap over Duterte's remarks started when a reporter asked him how he intends to explain the extrajudicial killings of drug dealers to Obama. More than 2,000 suspected drug dealers and users have been killed since Duterte launched a war on drugs after taking office on June 30.

In his typical foul-mouthed style, Duterte responded: "I am a president of a sovereign state and we have long ceased to be a colony. I do not have any master except the Filipino people, nobody but nobody. You must be respectful. Do not just throw questions. Putang ina, I will swear at you in that forum," he said, using the Tagalog phrase for "son of a bitch."

Duterte has previously cursed Pope Francis and UN Secretary-General Ban Ki-moon.

"Who is he (Obama) to confront me?" Duterte said, adding that the Philippines had not received an apology from the United States for misdeeds committed during its colonisation of the country.

He pointed to the killing of Muslim Moros more than a century ago during a US pacification campaign in the southern Philippines, blaming the wounds of the past as "the reason why (the south) continues to boil" with separatist insurgencies.

Last week, Duterte said he was ready to defend his bloody crackdown on illegal drugs, which has sparked concern from the US and other countries.

Duterte said he would demand that Obama allow him to first explain the context of his crackdown before engaging the US president in a discussion about the deaths.

Duterte has had a troublesome relation with the United States, questioning its inability to stop genocidal killings in the Middle East and Africa, and citing US police shootings of black Americans that have set off protests.

He has also taken on a more conciliatory position with US rival China. Philippines-China ties were strained under Duterte's predecessors due to territorial conflicts in the South China Sea. Duterte proclaimed early in his presidency that he would pursue a foreign policy not dependent on the United States.

Former Philippine Foreign Secretary Albert del Rosario, under whose watch US-Philippine relations blossomed, expressed disappointment over the aborted meeting with the US.

"An invaluable occasion to have our leaders meet for the purpose of discussing how to strengthen our comprehensive areas of cooperation would have been a golden opportunity," del Rosario said.