( CNN ) -- Security forces aboard a U.S. naval vessel fired warning shots toward two approaching small boats off the Somali coast Tuesday , the U.S. military said Wednesday . The USNS John Lenthall is one of 14 fleet refueling ships operated by Military Sealift Command . The rounds landed in the water , prompting the boats to turn around , and no casualties were reported , the military news release said . It is unclear whether the boats were trying to attack the 41,000-ton USNS John Lenthall , the military said . `` It is clear they were not following the international rules of the road observed by mariners around the globe , '' it said . The release noted that the location of the incident , the types of boats involved and the maneuvering were all `` consistent with reports from previous attacks on merchant vessels in the region . '' The USNS John Lenthall is one of 14 `` fleet replenishment oilers '' in the Military Sealift Fleet Support Command , according to a U.S. Navy Web site . Oilers refuel Navy ships at sea and any aircraft they may be carrying . Attacks by pirates have increased dramatically off the northern coast of Somalia in the past year , prompting the United States and other nations to step up patrols in the region . In May , the U.S. Navy warned merchant ships to stay at least 200 miles off the Somali coast . But the U.S. Maritime Administration warns that pirates sometimes issue false distress calls to lure ships closer to shore . The pirates are often armed with automatic rifles and shoulder-fired rockets , according to warnings from the agency .
Warning shots fired after two days raise suspicions of pirates . Boats were attacking a US Navy patrol ship . Warning shots land in water and boats turn away , CNN says . Pirates known to be just off African nation of Somalia .