Turkey expects the US to stop "shifting" YPG fighters from Manbij to Afrin in Syria, presidential spokesman Ibrahim Kalin said Wednesday.

Speaking to reporters at the presidential complex in the capital, Ankara, Kalin said: "It is particularly expected [by Turkey] that the US must certainly step in and halt the shifting of YPG/PYD forces, which move under its control, in Manbij to Afrin. This is our natural right.

"With this regard, we [Turkey] took the necessary steps via official channels, and we will continue to take [such steps]."

US partner

On January 20, Turkey launched a military operation against the YPG militia from Afrin.

Turkey sees the YPG - trained, armed and supported by the US to fight against ISIL - as an extension of the outlawed Kurdistan Workers Party (PKK).

The US has about 2,000 soldiers based in Manbij - 100 kilometres east of Afrin - and, in January, it announced that it will train about 15,000 fighters to be part of a 30,000-strong border force in the region.

As part of its ongoing operation, Turkey said it will eventually launch a military operation against the YPG in Manbij, also.

According to the Turkish General Staff, the operation aims to establish security and stability along the Turkey-Syria borders.