The US has issued a formal complaint to the Chinese government over the use of high-grade lasers near the military base in Djibouti that were directed at aircraft and resulted in minor injuries to two American pilots, the Pentagon said Thursday.

Pentagon spokeswoman Dana White said that the U.S. is confident that Chinese nationals are responsible for the use of the lasers, which targeted aircraft on several occasions in the last few weeks. White said the incidents represent a serious threat to U.S. airmen, and that the U.S. has asked China to investigate the incidents, USNews reported quoting AP.

She estimated there have been fewer than 10 laser incidents in recent weeks, and the Pentagon sought the formal complaint because of the injuries and the growing number of instances the problem happened.

Marine Lt. Col. Chris Logan, a Pentagon spokesman, said that reports from pilots indicate that on three occasions the lasers were military grade and came from the Chinese base nearby.