NATO vessels deployed in the Aegean Sea to help stop the flow of migrants into Europe have not yet started operating in Turkish waters and are waiting for the go-ahead from alliance member Ankara, diplomats told AFP Tuesday.

Despite requests by the NATO operation's German command, "the Turks refused" this weekend to allow the vessels to enter into Turkish waters, a diplomatic source told AFP.

Another diplomat confirmed the report.

The unprecedented mission, which seeks to tackle migrant smugglers, was launched earlier this month and aims to help the European Union cope with its worst migration crisis since World War II.

The plan is for the NATO force to conduct reconnaissance, monitoring and surveillance to provide information to Greece, Turkey and the EU's border agency Frontex so that they -- not the alliance -- can deal with the traffickers.

Longstanding disputes between Athens and Ankara over Aegean airspace and territorial waters have however held up agreement on the operational details.

Turkish authorities have now asked Rear Admiral Jorg Klein, the German commander of the NATO operation, "to go to Ankara to determine the area where (NATO) might deploy", the diplomatic source said.

"That is now being discussed between the Germans and the Turks," the source added.

Turkey meanwhile "is showing little to no interest" in taking back migrants picked up by the NATO vessels at sea as they attempt to make the perilous crossing to Greece, the source said.

Plans for the mission were first laid out in a meeting between German Chancellor Angela Merkel and Turkish Prime Minister Ahmet Davutoglu in Ankara on February 8.

Three days later, defence ministers from NATO's member states gave their go-ahead to start preparing the operation, and to the immediate deployment of three vessels in the Aegean.

More than a million migrants fleeing war in Syria and upheaval across the Middle East, Asia and Africa landed in the European Union last year, the bulk of them making the perilous journey across the Aegean from Turkey to Greece.