WASHINGTON (AFP) - US Defence Secretary Jim Mattis on Sunday (Jan 21) began a one-week trip to Asia, hoping to strengthen defence cooperation with Indonesia and Vietnam as regional Chinese military power looms ever larger.

"We share the Pacific - it's an ocean named for peace - we would like to see it remain peaceful, so all the nations that use it and live here are prosperous," Mr Mattis told reporters accompanying him on a military plane headed to the region.

In Jakarta, where he is to arrive Monday evening, Mr Mattis is to meet on Tuesday with President Joko Widodo and Defence Minister Ryamizard Ryacudu for talks on maritime cooperation.

The vast Indonesian archipelago reaches from the Indian Ocean to the Pacific.

In Vietnam, Mr Mattis and his counterparts are set to discuss freedom of movement in the South China Sea, a region over which Beijing has extended its dominance in recent years, militarising several small, disputed islands.

Washington hopes to draw a contrast between its own approach and those of China - seen as aggressively modernising its military capacities - and Russia, which has annexed parts of Georgia and Ukraine.

"The point I want to make is, we respect Asia's sovereign nations with a sovereign voice and sovereign decisions, and we don't think anyone else should have a veto authority over their economic, their diplomatic or their security decisions," Mr Mattis said.

"We respect these countries."