The US ambassador to the Philippines, Philip Goldberg, has warned that Philippine President Rodrigo Duterte's rhetoric about his nation's "separation" from the United States is becoming a concern around the world.

"It's clear that many of the things that have been said are inconsistent with friendship and alliance so we are trying to sort out exactly what that means in policy terms, what that means in terms of our relationship ongoing." "It is of course of concern as is some of the rhetoric we hear," he said.

US assistant secretary of state for East Asian and Pacific Affairs, Daniel Russel, met with Philippine defense and foreign ministers on Monday, after Duterte's remarks last week. Duterte quickly backtracked from his comments, saying he did not plan to sever his country's seven-decade old alliance with the United States.

Russel signalled that many people around the world were becoming increasingly worried about the Duterte's repeated tirades. He said US Secretary of State, John Kerry, rang Philippine Foreign Secretary, Perfecto Yasay, on Monday to discuss the alliance.