US Vice President Mike Pence said there was "no place for empire and aggression in the Indo-Pacific," in an apparent reference to China's growing influence in the region and its sweeping claims in the disputed South China Sea.

Pence was in Singapore to meet with heads of state from the 10-member Association of South East Asian Nations (ASEAN) and their Asia-Pacific counterparts at the East Asia Summit on Thursday. 

China has claimed much of the South China Sea, building military installations within its oil- and gas-rich borders, even as the Philippines, Taiwan, Vietnam and Malaysia have laid competing claims to the key maritime corridor. 

Washington has long maintained that freedom of navigation in the disputed waters is in accordance with international law, while Beijing claims that US joint military exercises in the territory are in violation of its sovereignty.

Defense Secretary Jim Mattis has said the US has told China that the US military will "fly, sail and operate wherever international law allows.”

Pence told ASEAN leaders on Thursday that the United States' commitment to the Indo-Pacific was "steadfast and enduring," assuaging fears that the US was loosening its engagement in the region. 

Donald Trump was notably absent from this week's ASEAN Summit, sending Pence in his stead. Pence will also attend the Asia-Pacific Economic Cooperation (APEC) forum beginning Saturday in Papua New Guinea.