Philippine President Rodrigo Duterte has apologised over his comments about President Barack Obama, after he referred to the US leader as a "son of a whore" to reporters.

"President Duterte explained that the press reports that the President Obama would 'lecture' him on extrajudicial killings led to his strong comments, which in turn elicited concern," Philippines Communication Secretary Martin Andanar said.

"He regrets that his remarks to the press have caused much controversy."

He added: "The President looks forward to ironing out differences."

The apology comes after President Barack Obama cancelled what would have been his first meeting with the outspoken Philippine leader.

A White House spokesman said that Obama told his aides to speak with Philippine officials to see if a meeting between the two of them would be "constructive" at this time.

Duterte referred to Obama as a "son of a whore" in front of reporters on Monday, just one day ahead of the planned meeting in Laos.

He said it would be "rude" for Obama to talk to him about human rights issues, and told reporters that a conversation along those lines would make him swear at the US President, using a Filipino phrase "putang ina" which can mean "son of a bitch" or "son of a whore".

He has only been president for a matter of months, yet Duterte's presidency is marred with inappropriate comments and extrajudicial killings as he wages war against criminals and drug dealers.

At least 2,400 people have been killed since he took office on July 1, including 900 in police operations against drug pushers.