A window fell off a U.S. chopper Friday at the U.S. naval air base in Atsugi, Kanagawa Prefecture, but no one was injured, Defense Minister Itsunori Onodera said.

The incident at U.S. Naval Air Facility, Atsugi, follows a similar one in Okinawa in December, when a window from a U.S. chopper plummeted onto the playground of an elementary school, nearly hitting some kids.

"While no one was injured and it's a case that happened inside a U.S. military base, a window falling is a serious problem," Onodera told reporters.