The United States, Australia, India and Japan recommitted to working together on Tuesday, after the first meeting of the China-focused "Quad" grouping's top diplomats since President Donald Trump returned to the White House.

On his first full day as secretary of state, Marco Rubio is meeting with his counterparts from a group of countries known as the Quad: the United States plus India, Japan and Australia, representing nearly 2 billion people and more than a third of global GDP.

The meeting, bringing together representatives of the four largest militaries in the Indo-Pacific, was a clear signal that the Trump administration will intensify military preparations and threats directed at China.