At least 129 children have been killed in the Philippines' four-year war on drugs, most by police or allied assailants, but they may only represent a fraction of the toll, activist groups said on Monday.

Minors have been directly targeted, punished as proxies, or victims of mistaken identity or "collateral damage," they said in a report, "How could they do this to my child?"

The World Organization against Torture (OMCT) and the Children's Legal Rights and Development Centre, a Philippines-based group, urged the U.N. Human Rights Council to launch an independent commission of inquiry into extrajudicial killings and other crimes at its three-week session opening on Tuesday.