Dozens of US Special Operations Forces have been deployed to Syria's border with Turkey to fight Daesh there, in support of the Turkish military and "vetted" Syrian rebels, the Pentagon said Friday.

Last month, Turkey launched Operation Euphrates Shield to improve security, support coalition forces and eliminate the terror threat along Turkey's border using Free Syrian Army fighters backed by Turkish armor, artillery and jets.

"At the request of the government of Turkey, US special operations forces are accompanying Turkish and vetted Syrian opposition forces as they continue to clear territory from ISIL in and around the area of the Syrian border near Jarabulus and Ar Rai," said Pentagon spokesman Jeff Davis.

That area is near the flashpoint city of Aleppo.

A US defense official said there were several dozen troops in the new special forces contingent.The Turkish military also said in a statement that U.S. special forces were supporting an operation that was being carried out between the Syrian towns of Azaz and al-Rai.

The chairman of the Joint Chiefs of Staff, General Joseph Dunford, discussed the fight against Daesh earlier with his Turkish counterpart General Hulusi Akar on the sidelines of a NATO chiefs of staff meeting in Croatia.

"General Dunford met with General Akar to advance discussions on the way forward in the fight against ISIL, and recommitted to the close military-to-military and strategic relationship the US has with Turkey," said Captain Gregory Hicks, a special assistant to the chairman of the Joint Chiefs of Staff.

The special forces deployment comes as Washington accused Damascus of blocking aid to besieged cities and warned it will not boost military cooperation with Russia unless Moscow is able to convince Assad both to halt attacks on opposition groups and allow humanitarian access.