Rome (CNN) -- Muslims who were among migrants trying to get from Libya to Italy in a boat this week threw 12 fellow passengers overboard -- killing them -- because the 12 were Christians, Italian police said Thursday.
Italian authorities have arrested 15 people on suspicion of murdering the Christians at sea, police in Palermo, Sicily, said.
The original group of 105 people left Libya on Tuesday in a rubber boat. Sometime during the trip north across the Mediterranean Sea, the alleged assailants -- Muslims from the Ivory Coast, Mali and Senegal -- threw the 12 overboard, police said.
Other people on the voyage told police that they themselves were spared "because they strongly opposed the drowning attempt and formed a human chain," Palermo police said.
The boat was intercepted by an Italian navy vessel, which transferred the passengers to a Panamanian-flagged ship. That ship docked in Palermo on Wednesday, after which the arrests were made, police said.
The 12 who died were from Nigeria and Ghana, police said.