"The Naval Criminal Investigative Service is investigating USS Ronald Reagan sailors for alleged unlawful drug possession, use and distribution," Katie Cerezo, public affairs officer for Naval Forces Japan, told AFP.

She declined to detail the number of sailors involved or what drugs they are suspected of distributing, citing the ongoing investigation.

"We take all reports of misconduct seriously, and are working with the appropriate Japanese law enforcement agencies," she added.

Military newspaper Stars and Stripes reported Tuesday that the carrier departed Yokosuka on what might be its last deployment before undergoing repairs.

In 2018, the Navy said it was investigating drug use by sailors at Yokosuka, and it removed three senior officers in southern Okinawa over "personal misconduct", which reportedly included drunkness.

Japan hosts around 50,000 US troops, most of them stationed at bases in southern Okinawa, where their presence has been controversial.