NATO says the alliance is expanding its mission in the Aegean Sea to stop the smuggling of migrants to Greece and into Europe.
The Associated Press quoted NATO Secretary-General Jens Stoltenberg as saying the alliance will operate in Greek and Turkish territorial waters, where smugglers have been bringing tens of thousands of migrants into Europe.
Stoltenberg told the news agency on March 6 that more ships will be on the way to the region to add to the three already there.
The statement came on the eve of a key summit in Brussels at which European leaders will persuade Turkey to accept "large-scale" deportations of economic migrants.
The European Union says Turkey has made progress toward implementing a cooperation-for-aid deal signed in November. But it said too many migrants were still heading from Turkey to Greece with nearly 2,000 arriving daily in February.
More than 400 have died or gone missing while attempting to reach Greece from Turkey aboard unseaworthy boats since the beginning of 2016.
Turkish media reported that at least 18 migrants drowned off the Turkish coast after their boat capsized on March 6. The Turkish Coast Guard rescued 15 others in the Aegean Sea, near the coastal town of Didim, the state-run Anadolu agency reported.
The victims' nationalities were not given.
Based on reporting by AP, AFP, dpa, and Reuters