The most senior U.S. diplomat for Asia assured the Philippines on Monday that Washington remained its "trusted" ally and that it supported Manila's blossoming ties with China.



U.S. Assistant Secretary of State for East Asian and Pacific Affairs Daniel Russel however warned that growing concern about drug-related killings in the Southeast Asian country was "bad for business".



Russel was the first high-level visitor from Washington after President Rodrigo Duterte provoked alarm last week by announcing his country's "separation" from the United States and realignment with China while on a visit to Beijing.



Explaining Duterte's "Goodbye America" remarks, Philippine Foreign Affairs Secretary Perfecto Yasay said on Saturday the United States remained the "closest friend" of the Philippines, but Manila wanted to break away from a "mindset of dependency and subservience" and forge closer ties with other nations.



Russel, speaking to reporters after meeting Yasay, said Duterte "has already walked back".



He said Washington supported direct dialogue and negotiations between the Philippines and China. "So, it's a mistake to think that improved relations between Manila and Beijing somehow come at the expense of the U.S.," he said.



"We don't want countries to have to choose between the U.S. and China."



During his meeting with the Philippine foreign minister, Russel however said he expressed his concern the "succession of controversial statements, comments and a real climate of uncertainty about the Philippines' intentions has created consternation in a number of countries".



He added, "This is not a positive trend."



Duterte has been scathing about U.S. criticism of his anti-drugs campaign in which about 2,300 people have been killed since he took office on June 30.



Russel said the United States supported Manila's anti-narcotics campaign, but due process and human rights should not be disregarded.



"The growing uncertainty about this and other issues is bad for business," he said. "This is a very competitive region."



Russel's trip to Manila is part of a three-nation swing through Southeast Asia that also includes Thailand and Cambodia, the U.S. State Department announced on its website.