(Edits, adds date of EU ministers' meeting on Libya, changes media identification slug)

By Robin Emmott and Francesco Guarascio

BRUSSELS, March 18 (Reuters) - Nearly half a million people displaced in Libya could travel to Europe, the EU's foreign policy chief has told the bloc's foreign ministers in a letter, urging action to prevent another escalation in the region's migration crisis.

In the message seen by Reuters, Federica Mogherini warned that people traffickers were operating freely in Libya and said the EU was working on sending a civilian security mission to boost the country's police, border forces and counter-terrorism operations.

The letter, sent on March 12, came in the build-up to a series of top-level meetings on the migration crisis, including one hosted by Britain in Brussels on Friday with Mogherini and leaders of France, Germany, Italy, Spain and Malta.

Diplomats and activists have said they are concerned Libya could be forgotten while the bloc focuses on reaching a deal with Turkey to return refugees from Greece. An effective deal with Turkey may also push traffickers to focus on other routes to smuggle migrants to Europe.

"There are more than 450,000 internally displaced persons and refugees in Libya who could be potential candidates for migration to Europe," Mogherini wrote.

SANCTIONS, SECURITY OPERATIONS

The European Union is working on helping Libya boost its institutions and on ensuring that a U.N.-backed government, currently based in Tunis, can operate from Tripoli.

The North African oil producer plunged into chaos after rebels ousted dictator Muammar Gaddafi in 2011, backed by British and French air strikes supported by the United States.

London and Paris struggled for months to win broader EU support for sanctions on three Libyan leaders seen as blocking the U.N. process to establish a government in Tripoli.

They finally won support this week to go ahead with preparations to impose asset freezes and travel bans, though the sanctions have yet to be adopted.

Beyond such measures, Mogherini said she was exploring "all possible options" that could help combat people traffickers in Libya. The EU and the United States hope they will be in a position to act quickly if a unity Libyan government is strong enough to call for foreign assistance.

EU defence and foreign affairs ministers will hold a joint meeting focussed on Libya on April 18 in Luxembourg to discuss Mogherini's plans, an EU official said on Friday.

"The possibility of setting up a team of 'deployable experts' on migration and security issues ... could be explored," Mogherini said in her letter.

Last June the EU deployed a military naval force in the central Mediterranean to counter traffickers who last year smuggled nearly 160,000 people from North Africa to southern EU shores, EU data show. (Reporting by Robin Emmott and Francesco Guarascio; Editing by Gareth Jones and Andrew Heavens)

By Steve Scherer

ROME, March 18 (Reuters) - Italian ships picked up some 600 migrants and recovered one body on Friday, as European leaders met in Brussels to try to stem the flow of migrants to the continent.

Italy's coastguard and navy tweeted that they had picked up the migrants from several different vessels. Rescue operations were continuing and the number was likely to rise, a coastguard spokesman said.

"Despite some bad weather and choppy sea conditions, the boats are coming," the coastguard spokesman said.

More than 1.2 million migrants, mainly from Africa and the Middle East, have arrived in Europe since the beginning of 2015. Arrivals from Libya have risen this week, when three bodies were recovered before the latest death.

"This year we are actually noticing a slight increase in the number of migrants arriving from Libya," Federico Soda, director of the International Organization for Migration Coordination Office for the Mediterranean, said in the statement.

"As of today, almost 12,000 migrants have landed in Italy, about 2,000 more compared to the number of migrants that arrived in the same period last year," he said.

European Union leaders are trying to put together an agreement to stem the flow of refugees from Turkey, which is hosting some 3 million Syrians fleeing war.

At the same time, EU leaders met to discuss ways to get Libyan factions to back a national unity government, which would clear the way to clamp down on people smuggling. (Additional reporting by Stephanie Nebehay in Geneva, editing by Larry King)