BEIRUT (Reuters) - A spokesman for the autonomous Kurdish region in Syria said on Monday that local military forces in the Syrian cities of Manbij and Jarablus are being reinforced, but not by Kurdish YPG militia.

The spokesman was responding to comments from regional security sources that YPG fighters appear to be reinforcing Manbij, captured this month from Islamic State, with weapons and personnel.

Manbij and Jarablus lie to the west of the Euphrates river, an area of northern Syria which Turkey and the United States have told the Kurdish YPG forces to withdraw from.

“There are reinforcements, but not by the YPG. Because the YPG are east of the Euphrates, not in Manbij or Jarablus,” said Ibrahim Ibrahim, head of the Rojava Media Office. Rojava is an autonomous political federation in northern Syria run by Syrian Kurdish parties and their allies.

He did not identify the forces being sent to Manbij and Jarablus, but he said military councils in both cities are made up of local fighters and some Free Syrian Army rebel groups which are allied to the U.S.-backed anti-Islamic State alliance the Syrian Democratic Forces (SDF).

The Kurdish YPG militia, which makes up a large part of the SDF, said it had withdrawn east of the Euphrates in line with U.S. and Turkish demands after the SDF drove Islamic State out of Manbij.

Turkey, battling its own Kurdish insurgency, wants to prevent Syrian Kurdish forces taking complete control of Syria’s northern border with Turkey.

NATO member Turkey regards the YPG as an extension of the outlawed Kurdistan Workers Party, or PKK, which has fought a three-decade insurgency for autonomy in Turkey’s largely Kurdish southeast. Washington considers the PKK terrorists but backs the YPG militia in the fight against Islamic State.

Last week Turkish-backed Syrian rebels and Turkish tanks entered Syria and seized the border town of Jarablus from Islamic State militants before pushing south into areas held by Kurdish-aligned militias.