Russia, Syria, and Turkey have lashed out at the United States for helping an allied Kurdish-led militia set up a 30,000-strong border security force in northern Syria.
"The United States has now acknowledged that it is setting up a terror army along our country's borders," Turkish President Recep Tayyip Erdogan said on January 15.
"What falls on us is to strangle this terror army before it is ever born," he said.
Erdogan said preparations for a military assault on the Kurdish-led forces in the Afrin region of northern Syria are "are complete" and an operation could start any moment, regardless of the presence of U.S. troops placed in the region to safeguard their allies.
Turkey has targeted Kurdish forces in areas near its border before, and the Syrian Observatory for Human Rights said on January 15 that Turkish artillery have been shelling Kurdish positions in the Afrin region for three straight days.
The U.S.-backed forces, known as the Syrian Democratic Forces (SDF), are an alliance of Arab and Kurdish militias dominated by the Kurdish YPG militia, which Ankara considers to be a terrorist group allied with armed Kurdish separatists that have been battling the government in Turkey for decades.
Syria's government also on January 15 warned the U.S.-backed SDF forces against consolidating their control over territory they regained from Islamic State (IS) militants in fighting last year, including IS's proclaimed former capital, Raqqa.
As a result of the fighting, the SDF currently controls nearly 25 percent of Syrian territory, all in the north and east of the country.
Damascus called the creation of the border force "a blatant attack on the sovereignty, territorial integrity, and unity of Syria, and a flagrant violation of international law."
Russia, which has given President Bashar al-Assad's government crucial support throughout Syria's civil war, agreed that the U.S. plan violates Syria's "territorial integrity" and warned it could lead to the "break-up of a large territory along the border with Turkey and Iraq."
"This is a very serious issue that raises concerns that a path toward the partition of Syria has been taken," Foreign Minister Sergei Lavrov said.
The U.S.-led coalition declined to comment on Lavrov's accusations or Erdogan's threat to "strangle" the new border security force.
It said in an e-mail to the Associated Press on January 15 that the security force is an important element of the coalition's strategy to prevent a resurgence of IS in Syria.
U.S. Defense Secretary Jim Mattis has said preventing a comeback by defeated IS militants is now the main U.S. goal in Syria.
"A strong border security force will prohibit [IS] freedom of movement and deny the transportation of illicit materials," the coalition told AP. "This will enable the Syrian people to establish effective local, representative governance and reclaim their land."
The coalition has said that its goal is to create a border security force with about 30,000 personnel "over the next several years," with about half the force comprise of SDF veterans.
The coalition said that about 230 individuals were currently undergoing training in the force's inaugural class.
Backed by the U.S.-led coalition's air strikes, advisers, and weapons, the SDF ousted IS militants from large swathes of northern and eastern Syria in a series of battles last year.
Its members now control territory bordering Turkey to the north, Iraq to the east, and Syrian government forces to the west.
With reporting by Reuters, AP, dpa, AFP, and the BBC