More than two dozen countries formally called on Thursday for a United Nations investigation into thousands of killings in Philippine President Rodrigo Duterte's war on drugs, activists said.

Iceland submitted the draft resolution backed by mainly European states, they said. The text urges the government to prevent extrajudicial executions and marks the first time that the Human Rights Council is being asked to address the crisis.

The Duterte government has insisted the more than 5,000 suspected drug dealers killed by police in anti-narcotics operations all put up a fight.