The so-called military coalition led by the United States in Syria is reportedly planning to set up a new large border force of up to 30,000 personnel with the aid of its militia allies in war-torn country, a move that will further infuriate Turkey, a NATO ally that is already angry over Washington’s strong support for Kurdish-dominated forces in the Arab country.

A top Turkish official, speaking on condition of anonymity, told Reuters on Sunday that the main reason behind summoning Philip Kosnett, the American charge d‘affaires in Ankara, last week was in fact Washington’s training of the new “Border Security Force” (BSF) within Syria, a move that was denounced by Turkish President Recep Tayyip Erdogan’s spokesman, who called it "worrying."

The force, whose inaugural class is presently being trained, would be dispatched to the borders of the area controlled by the US-backed Syrian Democratic Forces (SDF), which is an alliance of militias in northern and eastern Syria largely dominated by the Kurdish People's Protection Units (YPG).

Ankara views the YPG as the Syrian branch of the Kurdistan Workers' Party (PKK), which has been fighting for an autonomous region inside Turkey since 1984.

The United States' military support for the militia first began under the administration of US President Donald Trump’s predecessor, Barack Obama, which provided the SDF with weapons and training.

Earlier this week, President Erdogan once again said his country was to continue its military operation in northern Syria to keep Kurdish militants away from Turkish borders.

The Reuters report also said the US-led coalition’s Public Affairs Office had sent an email to the news agency, confirming the details of the new force, which had also been reported earlier by The Defense Post. It said, further citing the email, that the SDF veterans would constitute around half of the would-be force and recruitment for the other half was under way.

The force would be deployed along the border with Turkey to the north, the Iraqi border to the southeast, and also along the Euphrates River Valley, which practically serves as the dividing line separating the SDF and the Syrian government, the report added.

The US "is taking worrying steps to legitimize this organization and make it lasting in the region," said Erdogan’s spokesman, Ibrahim Kalin, adding, “It is absolutely not possible for this to be accepted.”

He also warned that his respective country would “continue its fight against any terrorist organization regardless of its name and shape within and outside its borders.”

The US-led coalition also claimed that the BSF would operate under the SDF command and some 230 individuals were currently undertaking training in its inaugural class.

Back in 2014, the US launched a so-called campaign against the Daesh Takfiri terrorist group together with a coalition of its allies. The military alliance has done little in the fight against the terrorists, and has instead been repeatedly accused of targeting and killing civilians and hampering Syrian government operations against Takfiri terrorists.

The Syrian government has in many occasions said the coalition has not gained any approval from Damascus to conduct its operations in the Arab country. Syria calls the coalition “an illegal occupation force” and its SDF allies as “traitors.”

In late December, Russia’s Foreign Minister Sergei Lavrov said the presence of American troops in Syria was unlawful, urging them to completely leave the Syrian soil.