Filipino and US troops began training exercises this week, the Philippines military said Wednesday, despite President Rodrigo Duterte's threats to end joint war games and kick American soldiers out of his country as he edges closer to Beijing.

Duterte has called for the withdrawal of American troops from his country and has branded US President Barack Obama a "son of a whore" in response to international criticism of his deadly war on drugs.

He also announced an end to joint war games after an amphibious exercise involving several hundred US and Filipino marines finished last month.

But on Wednesday, military spokesmen told AFP about an ongoing month-long joint training exercise involving around 30-40 Filipino solders and an unspecified number of US Special Forces.

"This is a very small bilateral activity," Filipino military spokesman Brigadier-General Restituto Padilla said, referring to the exercise that kicked off on Monday on the island of Palawan in the west of the archipelago.

Philippine Army spokesman Colonel Benjamin Hao earlier told reporters that the exercise was intended "to test the basic war fighting skills of our soldiers (and) to improve the relationship of both armed forces".

Harry Harris, commander of the US Pacific Command, said in Washington that military cooperation between the US and the Philippines is unchanged for now.

The Philippine military said it was awaiting guidelines from Duterte on whether the joint war games with its key defence ally would continue to be held next year. The country hosts 28 such exercises annually.

Duterte has made no secret of his hostility for the US, calling for US Special Forces to leave the Philippines' troubled Mindanao region where they currently train Philippine soldiers in counter-terrorism.

He has also threatened to scrap a defence pact intended to counter Chinese expansion in the South China Sea as he courts Beijing for aid and investment.

Duterte's war on drugs has seen more than 4,000 people killed, with the United Nations, the European Union and rights groups raising concerns about alleged extrajudicial killings and a breakdown in the rule of law.

Duterte has insisted he is not doing anything illegal, but added he would be "happy to slaughter" three million drug users.