Militant jihadists are said to be travelling on cruise ships to get to areas of conflict in the Middle East.
Interpol said that increasingly people trying to reach militant groups were resorting to take cruise liners to get to countries such as Turkey.
But the international police force did not give a number for how many militants had travelled this way. Its outgoing chief, Ronald Noble, said countries should conduct checks on all passengers using airports "and, more and more, cruise lines".
The Turkish government claims hundreds of suspected foreign jihadists have been deported in recent months. The suspects were apprehended at airports and bus stations.
Interpol said that this had led prospective fighters to try other travel means in an effort to avoid detection.
Regular stops at ports in the region would let the militants disembark undetected and make their way to Syria or Iraq untracked by security agencies.
"There is evidence that the individuals, especially in Europe, are travelling mostly to [the Turkish coastal town of] Izmit and other places to engage in this type of activity," s spokesman said.
Interpol officials said the militants' use of cruise ships had emerged only in the "past three months or so".
The Cruise Lines International Association (CLIA) said passenger manifests were already screened and systems were in place to confirm passengers' identities.
"Cruise lines employ full-time security professionals, many of whom are former law enforcement officers, who are in regular contact with local and international authorities," said the CLIA in a statement.
A recent United Nations report estimated there were 15,000 foreign jihadists from more than 80 countries fighting with Islamic State (IS) and other extremist groups in Syria and Iraq.
