Seoul: North Korea remains Washington's "number one security concern" in Asia, the US Pacific Fleet commander said on Wednesday, despite simmering territorial disputes elsewhere in the region.
Admiral Harry B. Harris Jr also accused China of "coercion" in its maritime disputes with neighbours.
He said an increased deployment of US military assets in the region as part of an Asian "pivot" announced in 2012 would ensure that "we are where it matters and when it matters".
"Our number one security concern is North Korea," Harris told reporters in Singapore on board the destroyer USS Spruance.
"I am concerned as a commander for the provocations that come from North Korea. I don't understand them, I don't understand their leadership and I don't understand their intent," he said.
Pyongyang last week warned of "calamities and disasters" if the United States and South Korea push ahead with a series of annual joint military drills from next month.
Last year's exercises were held in the wake of North Korea's third and largest nuclear test, and prompted months of escalated military tensions that saw Pyongyang issue similar apocalyptic threats of nuclear war against its southern neighbour and the United States.
Harris also expressed concern at China's declaration of an "air defence identification zone" over the East China Sea, including over islands disputed with Japan.
"We think that the air defence identification zone (ADIZ) was an unfortunate imposition in the region," he said.
"It highlights an issue that I am concerned about, and that is coercion by China in this case and other countries as well," he added.
"It has not affected our military operations at all. We choose to do business as usual in the ADIZ."
The declaration, which caused an international furore, requires foreign aircraft to declare their intentions and maintain communications with Chinese authorities or face unspecified "defensive emergency measures".
China is also embroiled in a bitter row with the Philippines, Vietnam and other nations about overlapping claims in the South China Sea.
Beijing claims sovereignty over essentially all that sea.
Harris urged countries involved in the territorial disputes to resolve them "amicably, peacefully, and without resort to undue pressure".
He also welcomed the acceptance by China's People's Liberation Army of an invitation to take part in major US-hosted naval drills for the first time in June off Hawaii.
The biennial Rim of the Pacific exerise, or RIMPAC, is billed as the world's largest international maritime war games and will feature armed forces from 23 nations.
"We welcome Chinese participation, and we welcome quite frankly the growth of China as a military power in the Pacific. There is nothing wrong with that," he said.