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

The 24-year-old man assigned to the nuclear-powered flattop based in Yokosuka, Kanagawa Prefecture, is suspected of smuggling 18 grams of synthetic drugs from Canada via Narita airport in December and January. 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 narcotics inside, the sources said. Drugs were also allegedly found in the apartment.

The U.S. Navy, already undertaking an investigation into drug use and dealing among sailors based in Japan, is also looking into the case to see where it fits in the wider problem.