WASHINGTON ― Two U.S. airmen suffered “minor” injuries as a result of the use of the Pentagon believes are Chinese-deployed lasers in Djibouti, the Defense Department’s chief spokeswoman said Thursday.

Dana White told reporters that the U.S. has formally lodged a diplomatic complaint, known as a demarche, with the Chinese government, requesting an investigation into the incident.

“This activity poses a true threat to our airmen,” White said. “It’s a serious matter, so we’re taking it very seriously.”

Maj. Sheryll Klinke, a Pentagon spokeswoman, confirmed to reporters after the briefing that the injuries were the result of one incident, in which two pilots of a C-130 aircraft were hit by a “military grade” laser. The pilots are not expected to suffer any long-term effects, Klinke said.

White did not have an exact number for how many incidents there had been, putting it between two and 10, all within the last few weeks. News of the injuries was first reported by the Wall Street Journal.

She did, however, indicate there were similar incidents in the past, where the U.S. did not take the formal step of issuing a diplomatic complaint. The decision to do so now was the result of “both” the injuries and the increased rate of incidents, White said.

The Pentagon is planning for war with China and Russia — can it handle both? War with China and war with Russia would have some overlapping qualities, but the Pentagon needs to figure out how and where to invest to deal with both.

Asked about potential motivation for the incident, White replied: “I’d have to ask you [to] ask the Chinese about the motivation. But it’s serious, we take it seriously, and that’s why we demarched them.”

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But the U.S. has been bracing for issues in Djibouti ever since China decided to open a military base just miles from Camp Lemonnier, currently the only permanent U.S. military base in Africa. China began construction of the base in March 2016 after it secured a 10-year lease for the facility.