China is deploying military assets to its man-made islands in the South China Sea in a strategy to intimidate its neighbours, US Defence Secretary James Mattis has said.
He said it "calls in to question, China’s broader goals".
General Mattis told the security summit in Singapore that China had deployed military equipment, including missiles, to the islands.
He said: "China’s militarisation of artificial features in the South China Sea includes the deployment of anti-ship missiles, surface-to-air missiles, electronic jammers and, more recently, the landing of bomber aircraft at Woody Island.”
Woody Island is also claimed by Vietnam and Taiwan.
Tensions in the contested South China Sea have risen in recent years after China embarked on an island-building campaign.
The economically important sea has overlapping claims by China, Vietnam, the Philippines, Malaysia, Taiwan and Brunei.
China's Lt Gen He Lei dismissed the comments as “irresponsible” while speaking at the same conference.
General Mattis said:
"Despite China's claims to the contrary, the placement of these weapon systems is tied directly to military use for the purposes of intimidation and coercion.
"China's militarisation of the Spratlys is also in direct contradiction to President Xi Jinping's 2015 public assurances in the White House Rose Garden that they would not do this."
The US defense secretary added: "Our Indo-Pacific strategy informs our relationship with China... China's policy in the South China Sea stands in stark contrast to the openness of our strategy.
"I believe there are much larger consequences in the future when nations lose the rapport of their neighbours, when they believe that piling mountainous debts on their neighbours and somehow removing the freedom of political action is the way to engage with them.
"If the US will continue to pursue a constructive results-oriented relationship with China, cooperation, whenever possible, will be the name of the game and competing vigorously where we must.”