The US has formally complained to China over several incidents of its pilots being irritated by lasers it says are coming from a Chinese base in Djibouti.
The Pentagon said it had asked China to investigate what it called “very serious incidents”.
Washington also said there would be consequences to “China’s militarisation of the South China Sea”.
Media reports have suggested China has stationed weapons systems on disputed islands in the region.
The US has a military base in Djibouti on the Horn of Africa, which is used for counter terrorism operations in Africa and the Middle East.
Last year, China opened its first overseas military base only a few kilometres from the US facility.
The Pentagon said people at the base had been shining military-grade lasers at US pilots coming in to land.
In one case, two pilots on a cargo plane suffered minor eye injuries, officials said.
“They are very serious incidents. We have formally démarched the Chinese government and we’ve requested the Chinese investigate these incidents,” Pentagon spokeswoman Dana White told reporters.
Ms White said the Pentagon was confident that while the intent was unclear, the lasers had been pointed by Chinese nationals.
In the past few weeks, fewer than 10 incidents had taken place, she said.
Meanwhile, the White House responded to reports of renewed Chinese activity in the South China Sea, including the reported stationing of military equipment on a number of disputed islands in the strategic water way.
“We’re well aware of China’s militarisation of the South China Sea,” White House spokeswoman Sarah Sanders said.
“We’ve raised concerns directly with the Chinese about this, and there will be near-term and long-term consequences.”
Several nations claim parts of the resource-rich South China Sea, but recent years have seen Beijing reasserting its claim.
China, Vietnam, the Philippines, Taiwan, Malaysia and Brunei all have competing claims.
Over the past years, the US has sent military vessels and aircraft to the region in what it describes as “freedom of navigation operations”.