By Ellen Francis and Jack Stubbs
BEIRUT/MOSCOW (Reuters) - Syria, Turkey and Russia responded vehemently on Monday to new U.S.-backed plans to set up a 30,000-strong "border force" inside Syria to protect territory held by Washington's mainly Kurdish allies.
The Syrian government vowed to drive the U.S. presence from the country. Turkey, an increasingly estranged U.S. ally within NATO, accused Washington of setting up a "terror army" on the Turkish border, and said it would take steps to protect itself.
Russia, the main ally of Syrian President Bashar al-Assad, said the U.S. plans revealed a plot to partition Syria.
The United States has led an international coalition using air strikes and special forces troops to aid fighters on the ground battling Islamic State militants in Syria since 2014. It has about 2,000 troops on the ground in Syria.
The U.S. intervention has taken place mainly on the periphery of a nearly seven-year civil war that has killed hundreds of thousands of people and driven more than 11 million from their homes.
Islamic State was effectively defeated last year, but Washington says its troops are prepared to stay to make sure the Islamist militant group cannot return, also citing the need for meaningful progress in U.N.-led peace talks.
The government of President Bashar al-Assad, backed by Russia and Iran, has made great strides over the past two years in defeating a range of opponents and has restored control of nearly all of Syria's main cities and towns. It considers the continued U.S. presence a threat to its ambition to restore full control over the entire country.
On Sunday, the U.S.-led coalition said it was working with its Syrian militia allies, the mainly Kurdish-led Syrian Democratic Forces (SDF), to set up a new 30,000-strong border force. The force would operate along the borders with Turkey and Iraq, as well as within Syria along the Euphrates River, which separates most SDF territory from that held by the government.
The plan has infuriated Turkey, which considers the Kurdish forces supported by the United States to be a threat to its national security. It says the Syrian Kurdish PYD movement and the affiliated YPG militia, which forms the main backbone of the U.S.-backed SDF force in Syria, are allies of the PKK, a banned Kurdish group waging an insurgency in southern Turkey.
"The USA...setting up a would-be terror army under the guise of a 'Syrian Border Security Force' amounts to playing with fire," Turkish Deputy Prime Minister Bekir Bozdag said on Twitter.
"The support which the USA has given to the Syrian PYD/YPG arm of the PKK terror group until now, and the steps which it has announced are not befitting a friendship, alliance, model partnership or strategic partnership," he said.
"Turkey will not refrain from taking the necessary measures and steps to protect our country and region's security. To use our president's expression: 'We may come suddenly one night.'"
Syria's main Kurdish groups have emerged as one of the few winners in the Syrian war and are working to entrench their autonomy over large parts of northern Syria. Washington opposes those autonomy plans, even as it has backed the SDF.
The Syrian government and the main Kurdish parties have mostly avoided conflict during the civil war, as both sides focused on fighting other groups. But Assad's rhetoric towards the Kurds has turned increasingly hostile.
Damascus denounced the new border force as a "blatant assault" on its sovereignty, Syrian state media said. It said any Syrian who joined the force would be deemed "a traitor".
"What the American administration has done comes in the context of its destructive policy in the region to fragment countries ... and impede any solutions to the crises," state news agency SANA cited a foreign ministry source as saying.
Russian Foreign Minister Sergei Lavrov said of the border force plan: "The actions that we see now show that the United States does not want to maintain the territorial integrity of Syria.
"Literally yesterday, a new initiative was announced about how the U.S. wants to help the so-called Syrian Democratic Forces create some border security zones. Fundamentally, this means the breakup of a large territory along the border with Turkey and Iraq."
The zone would be controlled by groups "under the leadership of the United States", he added. "This is a very serious issue that raises concerns that a path towards the partition of Syria has been taken," he said.
The coalition said the Border Security Force would operate under SDF command, and about 230 individuals were currently undergoing training in its inaugural class.
Its ethnic composition will reflect the areas in which the force serves. More Arabs would serve along the Euphrates River Valley and the Iraqi border, and more Kurds would serve in areas of northern Syria, the coalition said.
(Additional reporting by Daren Butler in Istanbul and Gabrielle Tetrault-Farber in Moscow; Writing by Tom Perry in Beirut; Editing by Peter Graff)