June 2 (UPI) -- U.S. Defense Secretary James Mattis warned Saturday there could be an aggressive U.S. response to China's military presence in the South China Sea.
Mattis warned there could be "much larger consequences" in the future from China's installation of weapons on disputed islands, the Wall Street Journal reported.
However, he did not say what the consequences would be.
The warning came in response to a question from an audience member after his speech at a regional security conference held in Singapore on Saturday. Mattis also talked tough on China during the speech.
Mattis said in his prepared remarks that "despite China's claims to the contrary, the placement of these weapons systems is tied directly to military use for the purposes of intimidation and coercion."
The annual conference, called the Shangri-La Dialogue, pulls together security officials, contractors and academics, CNN reported.
China has increased military activity in the islands this past month, and the United States has responded by sending two Navy warships into the sea in a freedom of navigation operation.
Senior Col. Zhao Xiaozhou, of China's People's Liberation Army's Academy of Military Sciences, suggested that the U.S. response could also be considered militarization.
Mattis stood on the United States' Indo-Pacific strategy.
"We do not do freedom of navigation for America alone, we do freedom of navigation for all nations," Mattis said. "We do not see it as a militarization by going through what has traditionally been international water space. We see it as affirmation of the rules-based international order."
"Make no mistake: America is in the Indo-Pacific to stay. This is our priority theater," Mattis added.
China was the main topic of conversation, though Mattis also briefly mentioned the planned June 12 meeting in Singapore between President Donald Trump and North Korean leader Kim Jong Un. Trump announced Friday that the meeting to discuss denuclearization was back a week after canceling it.