MANILA (REUTERS) - A Philippine senator challenged President Rodrigo Duterte on Thursday (Dec 6) to take a drug test after he joked about using marijuana during a regional summit in Singapore.

Mr Duterte, whose controversial war on drugs has killed nearly 5,000 suspected drug dealers and users since 2016, said on Monday that he used marijuana to stay awake - and then said he was just joking.

Marijuana is illegal in the Philippines and critics said Mr Duterte's attempt at humour could upset the relatives of those who died in the anti-drug campaign.

"Now, if he really wants to clear himself, I am calling again on him to take a drug test," opposition senator Antonio Trillanes said in a statement.

Mr Duterte's spokesman Salvador Panelo told a news briefing the President would not take up the challenge. "He should be the one taking the test," he said, referring to Mr Trillanes.

In a speech on Monday, Mr Duterte said he used marijuana "to keep me awake" at the Asean summit in Singapore last month, where he skipped several meetings.