The salvoes follow a fractious EU summit in June which agreed to set up "disembarkation platforms" outside the bloc to process migrants after Italy's new populist government said it was closing its ports.

"Italy does not want to be the only country where migrants saved at sea by its own naval units disembark," Foreign Minister Enzo Moavero Milanesi said in a letter to EU foreign policy chief Federica Mogherini.

The Italian position and its implications was to be discussed at a meeting later Friday by member states in Brussels, EU sources said. 

Libyan Prime Minister Fayez al-Sarraj meanwhile rejected the EU proposal for asylum processing centres in his country, saying: "We are strictly against Europe officially placing illegal migrants who are no longer wanted in the EU in our country."

Egypt, Morocco and Tunisia were also approached by the EU but have already refused to host such centres.

"We also won't agree on any deals with EU money about taking in more illegal migrants," the Libyan premier told Germany's Bild newspaper.

Sarraj said European leaders should instead put pressure on migrants' origin countries to stop them embarking on their journey in the first place. Most of the migrants are from the Middle East, Africa and South Asia.

Italian Prime Minister Giuseppe Conte has written to European Commission President Jean-Claude Juncker saying his country would no longer take in migrants plucked from the Mediterranean until other member states accepted some of them.

Over the last decade, the Italian coastguard has coordinated the rescue of hundreds of thousands of migrants off the coast of Libya, in many cases pulling them from the water themselves in treacherous conditions. 

But as of June, they have been ordered to transfer calls for help and reports of boats in distress to the Libyan capital Tripoli. 

Ad hoc solutions won't work 

Juncker wrote back to Conte saying "these ad hoc solutions will not be feasible in the long term," according to a copy of a letter seen by AFP.

But Juncker agreed to try and identify nations that would shelter rescued migrants until a definitive framework was agreed upon as to who would take charge of them.

June was the deadliest month in the Mediterranean in recent years with the International Organization for Migration (IOM) reporting some 564 deaths or disappearances, despite the fact that overall departures have dropped sharply since the summer of 2017.

Under a controversial deal with the EU, Libyan coastguards intercept migrants trying to cross the Mediterranean.

But the UN has slammed the policy as "inhuman", noting that the migrants are simply brought back to "horrific" detention centres in Libya.

The European Court of Human Rights also opposes the repatriation of migrants to Libya on the ground that they could face rights abuse.

The European Commission, the EU's executive arm, will discuss in the coming weeks proposals for controlled holding centres for migrants in member states and cooperation in rescue efforts, spokeswoman Natasha Bertaud said earlier this week.