By Robin Emmott and Francesco Guarascio
BRUSSELS (Reuters) - The European Union will help rebuild Libya's shattered navy and coastguard to tackle migrant smugglers after a plea for aid from the new U.N.-backed unity government in Tripoli, EU foreign ministers agreed on Monday.
Details of the aid are still to be worked out but EU foreign policy chief Federica Mogherini said an operational plan should come "in the coming days".
The ministers said they would need a U.N. Security Council resolution to go after arms traffickers on the high seas, but Monday's meeting signaled they were determined to stop migrant smugglers by using the EU's "Operation Sophia" mission in the Mediterranean.
Libya is a major departure point for mainly sub-Saharan African migrants trying to reach Europe through crossings arranged by people smugglers, often in flimsy boats.
The flow of migrants has increased amid the turmoil that followed the 2011 uprising that toppled Muammar Gaddafi.
With calm summer weather approaching in the Mediterranean, Europe's governments are keen to avoid the migrant drownings of last year and to deter smugglers finding new routes into Europe after a deal between the European Union and Turkey cut trafficking across the Aegean Sea.
Ministers underscored "the need to enhance the capacity of Operation Sophia to disrupt the business model of human smugglers and trafficking networks and to contribute to broader security in support of the legitimate Libyan authorities."
U.N.-backed Libyan Prime Minister Fayez Seraj, who has yet to establish his government beyond Tripoli, wrote to Mogherini to request the naval support, as well as possibly training for Libyan security personnel.
While Seraj's request remains broad, governments are divided about how far to go in Libya. The United States said last week it wants to see NATO do more to help the EU's naval mission, a position Britain shares.
"The Libyan coastguard is the basis on which we have to build security in the coastal waters of Libya," British Foreign Secretary Philip Hammond told reporters. "We can provide training, we can provide equipment, we can provide additional technical support."
The Sophia mission operates in international waters near Libya, but is too far out to destroy boats used by people smugglers, catch traffickers or head off migrants trying to reach Europe by sea from Libya.
Italy, Libya's former colonial power, has said it is willing to send around 5,000 personnel to help the country. But Germany and France say any action to train police and border guards must be in concert with NATO and the United Nations.
One of the biggest hurdles is what to do with migrants rescued close to North African shores, who cannot be safely returned to Libya because of the chaos in the country.
(Reporting by Robin Emmott; Editing by Janet Lawrence)