BRUSSELS (Reuters) – NATO ships are on their way to the Aegean Sea to help Turkey and Greece crack down on criminal networks smuggling refugees into Europe, the alliance’s top commander said on Thursday.

Hours after NATO defense ministers agreed to use their maritime force in the eastern Mediterranean to help combat traffickers, Supreme Allied Commander Gen. Philip Breedlove said he was working quickly to design the mission.

“We are sailing the ships in the appropriate direction,” Breedlove told a news conference, and the mission plan would be refined during the time they were en route. “That’s about 24 hours,” he said.

The plan, which was first raised only on Monday by Germany and Turkey, took NATO by surprise and is aimed at helping the continent tackle its worst migration crisis since World War Two. More than a million asylum-seekers arrived last year.

Unlike the EU’s maritime mission off the Italian coast, which brings rescued migrants to Europe’s shores, NATO will return migrants to Turkey even if they are picked up in Greek waters.

Britain’s defense minister said that marked a significant change in policy. “They won’t be taken to Greece and that’s a crucial difference,” Michael Fallon told reporters.

NATO will also monitor the Turkey-Syria land border for people-smugglers, said NATO Secretary-General Jens Stoltenberg.

Although the plan is still to be detailed by NATO generals, the allies are likely to use the ships to work with Turkish and Greek coastguards and the European Union border agency Frontex.

“There is now a criminal syndicate that is exploiting these poor people and this is an organized smuggling operation,” U.S. Secretary of Defense Ash Carter told reporters.

“Targeting that is the way that the greatest effect can be had … That is the principal intent of this,” Carter said.

The numbers of people fleeing war and failing states, mainly in the Middle East and North Africa, show little sign of falling, despite winter weather that makes sea crossings even more perilous.

A 3 billion euro ($3.4 billion) deal between the EU and Turkey to stem the flows has yet to have a big impact.

SEEKING SHIPS

Germany said it would take part in the NATO mission along with Greece and Turkey, while the United States, NATO’s most powerful member, said it fully supported the plan.

The alliance’s so-called Standing NATO Maritime Group Two has five ships near Cyprus, led by Germany and with vessels from Canada, Italy, Greece and Turkey. Breedlove said NATO would need allies to contribute to sustain the mission over time.

Denmark is expected to offer a ship, according to a German government source. The Netherlands may also contribute.

“It is important that we now act quickly,” German Defence Minister Ursula von der Leyen said.

Intelligence gathered about people-smugglers will be handed to Turkish coastguards to allow them to combat the traffickers more effectively, rather than having NATO act directly against the criminals, diplomats said.

Greek and Turkish ships will remain in their respective territorial waters, given sensitivities between the two countries.

NATO and the EU are eager to avoid the impression that the 28-nation military alliance is now tasked to stop refugees or treat them as a threat.

“This is not about stopping or pushing back refugee boats,” Stoltenberg said.

(Additional reporting by Sabine Siebold in Brussels and Michele Kambas in Athens,; Editing by Mark Trevelyan)