Presidential Spokesperson Ibrahim Kalın said Sunday that Turkey reserves its right to intervene against terror threat after US-led coalition confirmed reports that it will form a 30,000-strong the People's Protection Units (YPG)-led Syrian Democratic Forces (SDF) border army.

Turkey will continue to take necessary measures to ensure its security in line with national interests, Kalın said.

"The United States is making concerning threats by attempting to legitimize and solidify the PYD terror group while it instead should cease the support," Kalın said in a statement.

The Ministry of Foreign Affairs also slammed the move. "US's unacceptable plan to form YPG-led SDF border force threatens Turkey's national security and Syria's territorial integrity," the ministry said in a statement. "We condemn US's insistence on this erroneous step."

President Recep Tayyip Erdoğan said after the reports that the country may launch a military operation on northern Syria's Afrin "in the coming days" and urged the U.S. to support its efforts.

Erdoğan said the operation against the Afrin enclave aims to "purge terror" from Turkey's southern border.

The coalition named the "new" army the Syrian Border Security Force (BSF). About 15,000 of the fighters will be SDF veterans as the fight against Daesh comes to a close. Another 15,000 will be recruited and trained in the near future. Currently, 230 individuals are training in the inaugural class, according to the coalition statement.

The coalition said the ethnic composition of the new border force would be relative to the areas in which it serves: "Efforts are taken to ensure individuals serve in areas close to their homes. More Kurds will serve in the areas in northern Syria. More Arabs will serve in areas along the Euphrates River Valley (ERV) and along the border with Iraq to the south."