Washington has been boosting its backing for Philippine counter-terror efforts since Islamic State supporters seized parts of the southern city of Marawi last year, sparking a deadly five-month battle.

The unmanned aerial vehicle system worth $13.2 million, including six drones, turned over to Philippine troops was the latest US military assistance.

"Assets like the ScanEagle will significantly improve the (Philippine military's) ability to detect terrorist activities, piracy activities, territory encroachment," US Ambassador to Manila Sung Kim told reporters, referring to the drones.

Philippine Defence Secretary Delfin Lorenzana said the system, equipped with cameras and aircraft that can fly for 24 hours, would support operations against militants in the south.

The southern region of Mindanao is home to several pro-IS groups, including those that attacked Marawi in May last year in fighting that claimed more than 1,100 lives and reduced large parts of the city to rubble.

These new drones are to be used for reconnaissance missions in defence, humanitarian assistance and disaster response, Lorenzana said.

"With a number of security issues confronting our country today, there is a need to upgrade our nation's armed forces," Lorenzana said.

President Rodrigo Duterte had sought to loosen the Philippines' 70-year alliance with the US in favour of closer ties with China and Russia.

His anger was partly driven by American criticism of his drug war, which has seen police kill thousands of people and prompted an International Criminal Court preliminary examination.

Relations have improved under US President Donald Trump, who has praised Duterte for his drug war but the Philippine leader has increasingly turned to Beijing and Moscow to boost one of Asia's weakest armed forces.

Duterte last month cancelled a deal to buy helicopters from Canada after Ottawa ordered a review over human rights concerns.

"Do not buy anymore from Canada and the US because there is always a condition attached," Duterte said at the time.

The US embassy did not immediately respond to requests for comment on whether the drones implied similar rights concerns.