Five Chinese Navy ships are sailing in international waters in the Bering Sea off Alaska, the Pentagon said on Wednesday, in an apparent first for China's military that came as U.S. President Barack Obama toured the U.S. state.
Pentagon spokesman Captain Jeff Davis said it was the first time the United States had seen Chinese navy ships in the Bering Sea.
"We respect the freedom of all nations to operate military vessels in international waters in accordance with international law," Davis said.
The appearance of the ships is an example of the expanding reach of China's navy and overlapped with a three-day visit by Obama to Alaska as part of his efforts to raise awareness about climate change.
Two U.S. defense officials, speaking on condition of anonymity, said the United States had identified a Chinese amphibious ship, a replenishment vessel and three surface combatant ships.
None of the ships had been seen acting in an unprofessional or unlawful manner, the officials said, adding that the United States had become aware of their presence in recent days.
White House spokesman Josh Earnest said no threatening activity had been detected, and added that the Pentagon was monitoring the movement of the ships "but the intent of this is still unclear."
China has ramped up defense spending to modernize its forces and wants to develop an ocean-going "blue water" navy capable of defending its growing interests as the world's second-largest economy.
On Thursday, China is to hold a massive military parade featuring some 12,000 troops, the highlight of events there marking 70 years since World War Two ended in Asia.
Dean Cheng, a China expert at the Heritage Foundation think-tank in Washington, D.C., said the presence of the ships in the Bering Sea was designed to send a message to Washington about China's growing military might.
"It is living up to what the Chinese have been saying, 'We are now a blue water navy. We will operate in the far seas and we are a global presence'," Cheng said.
Melting sea ice has spurred more commercial traffic and China has sought to become more active in the Arctic, where it has said it has important interests.
Shorter shipping routes across the Arctic Ocean would save Chinese companies time and money.
It was not clear whether the presence of the Chinese ships was timed to coincide with Obama's visit or if it followed a recent Chinese-Russian navy exercise.
While the world's two largest economies have important mutual interests, like trying to rein in North Korea's nuclear program, disagreements exist between them including over China's claims in the South China Sea.
China's military buildup, which includes developing stealth fighters and anti-satellite missiles, has unnerved the Asia-Pacific region and Washington, especially since President Xi Jinping took office in 2013 and started taking a tougher line on maritime territorial disputes.
Xi is expected to spend about a week in the United States during the second half of September.
The Heritage Foundation's Cheng said the presence of the ships in the Bering Sea sent a message ahead of Xi's visit, which has been preceded by threats of U.S. action over cyber attacks.
"That message is, in a nutshell, 'Stop pushing us. We are not going to be lectured'," Cheng said.