The EU is preparing to step up action against people smugglers in the Mediterranean, actively seizing the boats which carry thousands of hapless migrants to Europe, officials said Tuesday.

The 28-nation EU launched the first, intelligence gathering phase of its EU NavFor Med operation in July and the commander Admiral Enrico Crendendino believes it is now time for the next step as the crisis deepens, they said.

"Based on his military assessment, (Crendendino) presented a proposal to move to the second phase of the operation," said Catherine Ray, spokeswoman for EU foreign policy chief Federica Mogherini.

Such action would still be confined to the high seas, in line with international law, she noted.

Ray added that Mogherini supported Crendendino's recommendation, which will be discussed by EU defence ministers on Thursday and then by the 28-nation bloc's foreign ministers at informal meetings in Luxembourg on Friday and Saturday.

Mogherini will chair both meetings as the European Union searches desperately for a solution to the flood of migrants fleeing war and turmoil across the Middle East and beyond.

"At this stage, there are frankly no reservations about moving on to this (second phase)," an EU diplomatic source told AFP.

"There is a group of countries who are clearly in favour" of proceeding, said another EU diplomatic source while a third cautioned that a "clearer case needs to be made" for action.

A third phase in the plan, agreed by EU leaders in May after more than 700 migrants drowned off southern Italy, allows EU NavFor Med to take military action against the people smugglers inside Libyan territorial waters, aiming to destroy their boats before they set sail.

This step however requires at a minimum a UN Security Council resolution and preferably Libyan government agreement.

EU efforts to help establish a national unity government in Libya have so far failed and there has been little mention of the UN resolution for some time.

EU NavFor Med currently comprises four ships -- one Italian, one British and two German -- and would likely need several more vessels for the enlarged mission.