The US and its Asian allies have expressed growing concern about China's increasing assertiveness in the Pacific, but Washington said the drills were not aimed at any country even though they would be significantly larger than previous exercises.

At least 4,000 US and Indonesian soldiers will be joined by forces from Australia and Singapore -- as well as Japan, which is participating for the first time in the annual drills, known as "Super Garuda Shield".

The exercise is taking place on the western parts of Sumatra and the Riau islands, a province of islets scattered near Singapore and Malaysia.

"This is really an exercise to build trust, build togetherness, mutual understanding, increase capability and other related matters," Major General Stephen Smith, commander of the participating US troops, told reporters in Jakarta on Friday.

"So this is really a military exercise and not a threat to any party."

The exercise comes as US House of Representatives Speaker Nancy Pelosi prepares to lead a congressional delegation to the region in the shadow of diplomatic tensions with China.

But her office made no mention of whether she would visit Taiwan, a flashpoint in conversations between Beijing and Washington ahead of the trip, which is expected to begin on Monday.

US President Joe Biden and Chinese President Xi Jinping held a tense phone call on Thursday, agreeing to schedule their first in-person summit but with Xi warning Washington not to "play with fire" in Taiwan.

The exercise will last until August 14 encompassing army, navy, air force and marine drills.

An opening ceremony with all participating nations will take place on Wednesday, an Indonesian official said.

Canada, France, India, Malaysia, South Korea, Papua New Guinea, Timor Leste, and Britain will participate as observer nations.