MANILA • President Rodrigo Duterte, who is known for his profanity-laced speeches, said God has told him to stop cursing.

In a press conference after an official visit to Japan, the Philippine leader told reporters about his late-night revelation during his flight home.

"As I was coming over here... everybody was asleep snoring. A voice said 'you know, if you don't stop, I will bring this plane down now.'

"And I said, who is this? 'Of course, it's God.' So, I promised God not to express slang, cuss words," he said on Thursday.

He said he wanted to keep his promise because "a promise to God is a promise to the Filipino people". When his audience applauded, he warned them: "Don't clap too much or I might fail."

Mr Duterte did not curse once during the hour-long press briefing at Davao airport, reported GMA News.

But when asked if he would no longer curse the United States, the European Union and opposition senator Leila de Lima, he replied: "There is always a time. A time to be foul-mouthed."

He said his actions were "all calibrated". In June, he made a similar pledge before his inauguration.

Then, he said he was enjoying his last moments as a "rude person", because "when I become president, when I take my oath of office... There will be a metamorphosis".

However, in the following months, he heaped scorn on his critics, calling them "sons of whores" and even telling US President Barack Obama to "go to hell".

He also cursed the EU after it urged him to launch an investigation into the rising death toll in his administration's war on drugs.