New threats from Pyongyang, ominous economic signals and China's aggressive stance on its territorial claims in the South China Sea and the Pacific have sent jitters through the region.
President Barack Obama's administration has long talked about a "re-balancing" in America's strategic focus, the so-called "pivot to Asia," but has often been distracted by crises elsewhere.
Officials say 21st century America will be as much a Pacific power as an Atlantic one, but in recent months Syria, Ukraine, Iran and Cuba have used up a lot of diplomatic bandwidth.
Later in the day, Foreign Minister Sushma Swaraj of India, the world's largest democracy and a growing economic partner of the United States, was also to meet her US and Japanese counterparts.
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"The primary purpose of this is to recognise that the region is going through certain challenges, but also faces major opportunities," US Secretary of State John Kerry said.
Kerry cited negotiations for the Trans-Pacific Partnership -- a major free trade deal -- as a great chance to deepen economic engagement, and North Korea's rogue regime as an immediate danger to the region.
"Let us deepen further our three countries' dialogue today as well and cooperation over wide areas, including security," he said.
South Korea's foreign minister, Yun Byung-se, said the meeting came "at a very critical juncture, when the eyes of the world are set on the major challenges involving all of us."
He said the talks would send a "very clear" message to North Korea in particular not to provoke the allies.
On October 10, North Korea will mark the 70th anniversary of its ruling Workers' Party and there has been speculation for months that it will celebrate with a long-range rocket test.
And even if the test does not take place, tensions remain high in the region, with Pyongyang periodically escalating its rhetoric and threatening all-out war against its neighbor.