Passengers on the ship told said they woke up to the sound of sirens at around 3 or 4 a.m. Wednesday, and one heard a request for medical assistance on one of its decks, according to KHOU.

"It is standard practice for the FBI to review deaths that occur on cruise ships," a spokesperson for Carnival shared in a statement with PEOPLE on Monday. "It does not automatically imply suspicious circumstances, and the facts of this matter do not suggest any such activitiy."