Under Operation Sophia, naval vessels will be able to board, search, seize and divert vessels suspected of being used for human smuggling.

Until now, the EU has 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.

However, many more migrants and refugees – mainly Syrians fleeing the country’s civil war – are taking a different route, crossing overland into Turkey, before a short journey by sea to European Union member Greece and onwards to central and northern European countries, with Germany the preferred destination.

The migrant crisis is expected to be one of the issues raised when German Chancellor Angela Merkel and French President Francois Hollande make a rare joint address to the European Parliament in Strasbourg on Wednesday.

The only previous such address was in 1989 with then French President Francois Mitterrand and the German leader Helmut Kohl.

Europe migrant crisis – in depth

Analysis: James Reynolds, BBC News, Rome

The limits of the EU’s mission are obvious. Its warships will have to stick to international waters – meaning that they will have to stay 12 nautical miles away from the Libyan coast.

It’s not immediately clear whether or not six warships, together with support helicopters and drones, will make a practical difference to the number of journeys begun by smugglers and migrants.

On some days, around 20 migrant ships set sail from the Libyan coast.

The EU eventually hopes to move to a third, more aggressive phase of its operation – by operating within Libya’s own territorial waters. But this will only be possible with the approval of either the UN Security Council or Libya itself.