The U.S. Navy is investigating an alleged drug ring involving a number of sailors based at the 7th Fleet’s headquarters in Yokosuka, Kanagawa Prefecture, it confirmed Saturday.

“Naval Criminal Investigative Service (NCIS) is investigating Yokosuka-based Sailors for alleged drug use and distribution,” 7th Fleet spokesman Cmdr. Clay Doss told The Japan Times in an email. “The Navy has zero tolerance for drug abuse and takes all allegations involving misconduct of our Sailors, Navy civilians and family members very seriously.”

He declined to comment further.

The Wall Street Journal had reported earlier that the U.S. Navy was investigating at least a dozen Yokosuka-based sailors, some serving aboard the USS Ronald Reagan aircraft carrier, on suspicion of buying, selling and using LSD, ecstasy and other drugs, it quoted navy officials as saying.

The navy was also probing whether U.S. sailors were using the internet to buy or sell drugs or were distributing them to Japanese residents.

The Journal report said the U.S. Navy first learned of the allegations on Tuesday, when it received a tip about a petty officer third class using drugs, the officials said. That sailor pointed investigators to others aboard the carrier who the sailor said were distributing or using drugs, it quoted a U.S. military official as saying. The official said others could be detained or charged in the continuing probe.

Japanese authorities have also been brought into the investigation because of suspicions that drugs were sold to residents, it quoted two U.S. Navy officials as saying. In addition, a suspicious package related to one of the sailors was intercepted by a local postal service, the report said, citing a navy official.

The 7th Fleet was plagued by a series of incidents involving its destroyers last year. The USS Fitzgerald struck a commercial ship off Yokosuka in June, killing seven U.S. sailors, and the USS John S. McCain collided with an oil tanker in coastal waters off Singapore in August, killing 10 U.S. sailors.

After the collisions, a series of reports and investigations revealed failures in training and readiness throughout the 7th Fleet. In January, the U.S. Navy said the commanders of the ships would face charges of negligent homicide. The Reagan returned to port in Yokosuka in December after a three-month deployment that saw it conduct joint exercises with the Maritime Self-Defense Force and the South Korean military amid North Korea’s growing missile and nuclear provocations. The vessel is currently undergoing regular maintenance.