Singapore (CNN) The United States can't fully trust China until Beijing starts playing by the rules. That was the overarching message delivered by acting US Defense Secretary Patrick Shanahan at Asia's premier defense forum Saturday morning in Singapore.

for using what he called a "toolkit of coercion" in the Indo-Pacific, which includes the controversial Speaking to hundreds of delegates at the Shangri-La Dialogue, Shanahan avoided calling China out by name, but criticized "some in our region"for using what he called a "toolkit of coercion" in the Indo-Pacific, which includes the controversial South China Sea

That toolkit included island-building, deploying advanced weapons systems to disputed areas, engaging in predatory economics and the alleged state-sponsored theft of military and civilian technology -- all activities the US has previously accused China of undertaking.

Beijing claims almost the entire 1.3 million square mile South China Sea as its sovereign territory and aggressively asserts its stake, with President Xi Jinping saying it will never give up "any inch of territory." US military officials, meanwhile, have vowed to continue enforcing a free and open Indo-Pacific.

Shanahan said that the Indo-Pacific region was the US's most important theater from a security perspective.

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