MANILA, June 15 ― Philippine President Rodrigo Duterte will not cooperate with an investigation of the Southeast Asian nation's drug war killings planned by the International Criminal Court (ICC), his spokesperson said today.

Rights groups and critics of the drug killings have welcomed the step by the ICC, saying a full-scale investigation will bring justice closer for the thousands of people killed in Duterte's bloody war on drugs.

"We will not cooperate because we are no longer a member,” Harry Roque told a news conference. Duterte cancelled the Philippines' membership of the ICC's founding treaty in March 2018.

"We do not need foreigners to investigate killings in the drug war because the legal system is working in the Philippines,” Roque said, adding he believed launching a formal probe was "legally erroneous and politically motivated.”

An ICC prosecutor sought authorisation on Monday to open a full investigation into the killings, saying crimes against humanity could have been committed.

"The long arm of the law will soon catch up with Duterte and his accomplices,” former opposition senator Antonio Trillanes said in a statement.

Since Duterte took office in 2016 until the end of April this year, police have killed more than 6,100 suspected drug dealers in sting operations, government data show.

Rights group say police were summarily executing suspects, but authorities say they were killed after violently resisting arrest. ― Reuters