Philippine President Rodrigo Duterte said on Wednesday that an upcoming military joint exercise with the United States would be the last between the two allies, but pledged to honor their longstanding security treaty.
The firebrand leader has strained ties with Washington in recent weeks, calling for the pullout of U.S. special forces stationed in the Philippines' restive south that he said were complicating counter-insurgency operations.
"I am serving notice now to the Americans, this will be the last military exercise," Duterte told a gather of the Filipino community in Hanoi, referring to next month's joint marine exercise with the Philippines' former colonial master.
Duterte added that there would be no chance of joint naval patrols with Washington and that the notion that there was conflict between the Philippines and China was "more imaginary".
The comments by Duterte, a former southern mayor known for his terse words and volatile temperament, add to uncertainty about what impact his rise to the presidency this year will have on one of Washington's most important alliances in Asia.
The Philippine military and U.S. Marines are due to hold annual amphibious landing exercises from Oct. 4 to 12 in the north of the Philippines main island Luzon.
Military leaders from the two countries have also started preparing for a new set of exercises next year.
Duterte said the Philippines would not join any patrols in the South China Sea to avoid getting dragged into a possible conflict between the United States and China, but would continue to honor their 1951 Mutual Defense Treaty.
This week, Duterte said he will open new alliances with China and Russia to increase trade and commerce as defense and foreign ministry officials have started exploring weapons deal with Moscow.
Richard Jacobson, an American security expert, said Duterte's posturing could embolden China, which is expected to exploit what it perceives as a crack in the U.S.-Philippines relationship.
"One could say that the U.S.-Philippines relationship might become strained and even shaken," Jacobson told Reuters, but he doubts if it will be broken.
"The U.S. geopolitical stakes in the region are much too high to react to his hyperbole. The current attitude in Washington is mature - more of patience than feeling provoked."
Duterte is hugely popular at home for his brash remarks and take-charge style, but his frequent tirades against Washington, including calling both President Barack Obama and his ambassador to Manila a "son of a bitch", have tested a relationship of strategic importance to both sides.
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The Philippines and the United States share concerns about China's pursuit of broad claims in the South China Sea, which overlap with those of Manila and other neighbors.
Washington and Manila agreed on joint patrols in the South China Sea before Duterte's election win this year, and a Pentagon spokesman said earlier this month three had been conducted from March until July.