The European Union has started an operation which will see naval vessels stop, search and if required, seize boats suspected of carrying migrants in the Mediterranean.
The operation, known as Operation Sophia, was launched today.
To date, the EU had focused on surveillance and rescue operations.
So far this year, more than 130,000 migrants and refugees have crossed to Europe from the north African coast. More than 2,700 have drowned.
Warships will operate only in international waters, but the EU is planning to eventually move to a third phase of the operation, involving action within Libyan territorial waters, from where the migrant boats depart. But that would require approval of the UN Security Council or Libya itself.
The EU operation has been called Sophia after a baby born to a rescued Somali woman on a German frigate in August.
Command and control will be coordinated from Rome.