The US ambassador to the Philippines on Tuesday called for "full accountability" following the alleged murder by local police of a 17-year-old boy as part of President Rodrigo Duterte's drug war.
The killing of Kian Delos Santos last week triggered rare protests against Duterte's controversial but popular campaign to eradicate drugs, with critics saying it highlighted rampant rights abuses by police enforcing the crackdown.
"My condolences go out to the family and friends of Kian. Hope that the investigations lead to full accountability," said Sung Kim, the American ambassador to Manila on his Twitter account.
Mr Duterte won an easy victory in the presidential elections last year after promising to wipe out drugs in the country by waging an unprecedented crackdown in which tens of thousands of people would die. Since he came into office 14 months ago, police have reported killing 3,500 people in anti-drug operations. More than 2,000 other people have been killed in drug-related crimes and thousands more murdered in unexplained circumstances, according to police data.
Under Barack Obama, the US president at the time, the United States, a longtime ally of the Philippines, led international criticism of Duterte's drug war.
Mr Duterte reacted furiously and used the criticism as a reason to loosen his nation's alliance with the United States, although he has said relations with the United States are better under Donald Trump, who has praised him for doing an "unbelievable job on the drug problem".
Ambassador Kim's predecessor had repeatedly criticised Duterte in public. Mr Kim, who arrived late last year in the Philippines as ambassador has sought to repair bilateral relations and refrained from criticising the drug war. While human rights groups say Mr Duterte may be orchestrating a crime against humanity, many Filipinos support the charismatic president and his efforts to fight crime.
However, the death of Delos Santos has dominated the media, and even some of Mr Duterte's supporters have spoken out against the killing.
Police said Delos Santos was a drug courier who fired at them while resisting arrest. However CCTV footage emerged of two policemen dragging the unarmed boy away moments before he was killed. The public attorney's office on Monday said a forensic investigation found Delos Santos was shot in his back and ear, and that the evidence pointed to an "intentional killing".
President Duterte has said any police officer convicted would be jailed. However, he president has also repeatedly vowed to pardon officers if they are found guilty of murder while fighting his drug war. Last month he ordered the reinstatement of policemen who the National Bureau of Investigation had accused of murdering a politician who was in a jail cell facing drug charges.