MANILA (Reuters) – The Philippines has filed a diplomatic protest with China, its foreign minister said on Monday, over Beijing’s installation last year of anti-aircraft and anti-missile systems on its manmade islands in the disputed South China Sea.

The protest note was sent to the Chinese embassy in December, after confirmation of a report from the U.S.-based Center for Strategic and International Studies about a weapons buildup on seven artificial islands in the Spratlys.

One of those islands is located within the Philippines’ 200 nautical mile exclusive economic zone.

Foreign Secretary Perfecto Yasay told CNN Philippines it was important to raise concerns carefully, and not create a big row.

“I just want to assure the Filipino people that when we take action at engaging China in this dispute, we do not want to take such aggressive, provocative action that will not solve the problem,” he said.

China claims almost the entire South China Sea, through which about $5 trillion worth of goods passes every year. An international arbitration ruling last year invalidated those claims.

Speaking up about that has become a tricky issue for the Philippines since President Rodrigo Duterte turned its foreign policy upside down by seeking engagement and a new relationship with China. Until recently the Philippines had been one of the most outspoken critics of Beijing’s maritime assertiveness.

“We cannot engage China in a war,” Yasay added, but “when there are reports about the buildup of weapon systems in the area during our watch, we made sure that the interests and rights of the Philippines are properly protected.”

The Philippines this year chairs the Association of South East Asian Nations (ASEAN) and Yasay said last week he was confident a protracted code of conduct between the grouping and China could be finished by mid-year, after 15 years and limited progress.

China’s artificial islands became a hot issue last week when the U.S. nominee for Secretary of State, Rex Tillerson, told a Senate hearing that Beijing should be repelled from, and then denied access to, the controversial islets.

Yasay last week suggested the Philippines would play no part in that, and said of the United States, “Let them do it”.

(Reporting by Manuel Mogato; Editing by Martin Petty and Clarence Fernandez)