A U.S. Navy sailor assigned to the aircraft carrier Ronald Reagan was referred to Japanese prosecutors on Monday for allegedly smuggling narcotic drugs by international mail, investigative sources said.

The 24-year-old man assigned to the nuclear-powered flattop based in Yokosuka, near Tokyo, is suspected of smuggling in a total of 18 grams of synthetic narcotic drugs from Canada via Narita airport in December 2017 and January of this year. He denied the charges during voluntary questioning, according to the sources.

Customs officials found a suspicious package addressed to the suspect's apartment in Yokosuka and detected the narcotic drugs inside, the sources said. Drugs were also found in the suspect's room.

The U.S. Navy is also undertaking an investigation into the alleged sale and use of drugs by a number of other sailors based in Japan.