The U.S. government is "cautiously optimistic" on Philippine President Rodrigo Duterte's war on drugs following a decline in extrajudicial killings, a U.S. senior narcotics official said Tuesday.

Washington has shifted away millions of dollars in funding for law enforcement from a drug control program of the Philippine National Police since the bloody anti-narcotics campaign started in July 2016.

But there are positive signs and the United States remains supportive of the Philippines' effort to battle illicit drugs, said James Walsh, a deputy assistant state secretary in the international narcotics and law enforcement bureau.