The Pentagon said Thursday the U.S. government has “formally demarched the Chinese government” after two American pilots were injured by Chinese military personnel directing lasers at U.S. aircraft near their adjacent bases in Djibouti.

“They are very serious incidents. There have been two minor injuries. This activity poses a true threat to our airmen,” Chief Pentagon Spokesperson Dana White told reporters Thursday.

“We have formally demarched the Chinese government, and we’ve requested that the Chinese investigate these incidents,” she said.

White refrained from speculating on the Chinese military’s motivations.

“I’m going to have you ask the Chinese about their motivations. But it’s serious, and we take it seriously, and it’s why we demarched them,” she said.

CNN first reported Thursday that Chinese personnel were using the lasers to interfere with U.S. military aircraft on separate occasions.

A notice to airmen issued by the U.S. noted that during one incident, there were two minor eye injuries of aircrew flying in a C-130 that resulted from exposure to military-grade laser beams originating from the nearby Chinese base.

The U.S. has about 4,000 personnel in Djibouti, due to its strategic location near terrorist hotspots Somalia and Yemen.

China formally established its first overseas military base in Djibouti last year, within sight of the U.S.’s military base.

Commander of U.S. Africa Command Gen. Thomas Waldhauser told Congress this year that the U.S. is “taking significant steps on the counterintelligence side so that we have all the defenses that we need there, there is no doubt about that.”