Donald Trump announces his candidacy for the U.S. presidency at Trump Tower in New York City.

U.S. President Donald Trump was notably absent when the ASEAN summit kicked off in Singapore this week — a sign Washington may not be "as committed to Asia" as its regional allies would like it to be, said Alex Capri, visiting senior fellow at the National University of Singapore.

U.S. Vice President Mike Pence is representing Trump at the 33rd Association of Southeast Asian Nations (ASEAN) summit, and is expected to lay out details of America's free and open Indo-Pacific vision during his Asia tour.

Trump's planned absence has raised questions about his commitment to Asia Pacific, as regional powers such as China, Japan and India seek to enlist support for a multilateral trading system.

The no-show signals that "the U.S. is maybe not as committed to the region as some of its allies would like to seem it," Capri told CNBC on Thursday.

"Optics are very very important — and statements and symbolisms. Who comes, what's on the table, what's on the agenda," said Capri. "If Trump were to come out I think it would have been a much more symbolic that ... this was more important."