The United States Coast Guard detected a Russian military ship on October 29 approximately 15 miles (24 kilometres) south of Oahu, near US territorial waters, it said on Thursday in a statement.
A Coast Guard aircraft and cutter, "responded to the Russian Federation Navy Auxiliary General Intelligence ship Kareliya," the Coast Guard said.
"Acting in accordance with international law, Coast Guard personnel are monitoring the Russian vessel's activities near US territorial waters to provide maritime security for US vessels operating in the area and to support US homeland defense efforts," the Coast Guard said.
The Coast Guard said under international law, foreign military vessels may, "transit and operate outside other nations’ territorial seas, which extend up to 12 nautical miles from shore."
The Russian embassy in Washington did not immediately respond to a request for comment.
(Reporting by Christian Martinez; Editing by Tom Hogue)