Ankara (Reuters): Turkey shelled targets in northern Syria on Monday and said it would swiftly crush the US-backed Kurdish YPG fighters who control the Afrin region, amid growing international concern over its three-day-old military operation.

Turkish forces and their Syrian rebel allies began their push to clear YPG fighters from the northwestern enclave on Saturday, opening a new front in Syria’s civil war despite calls for restraint from United States.

France has called for an emergency meeting of the United Nations Security Council on Monday to discuss the fighting in Afrin and other parts of Syria .

The YPG’s Afrin spokesman, Birusk Hasaka, said there were clashes between Kurdish and Turkey-backed forces on the third day of the operation. He said Turkish shelling had hit civilian areas in Afrin’s northeast.

Ankara considers the YPG a terrorist organization tied to Kurdish militant separatists in Turkey and has been infuriated by US support for the fighters. Washington, which has backed the YPG in the battle against Islamic State in Syria , said on Sunday it was concerned about the situation.

Turkish anger at US support for the YPG is one of a number of issues that have brought relations between the United States and its biggest Muslim ally within NATO to the breaking point in recent months.

President Tayyip Erdogan has pledged to crush the YPG in Afrin, and also says he will target the Kurdish-held town of Manbij to the east, part of a much larger swath of northern Syria controlled by YPG-dominated forces.

That raises the prospect of protracted conflict between Turkey and its allied Free Syrian Army factions against the Kurdish YPG, who spearheaded the US-backed campaign to drive Islamic State out of its Syrian strongholds last year.

Turkish Deputy Prime Minister Mehmet Simsek played down the potential for a damaging and drawn-out military campaign.

“Our investors should be at ease, the impact will be limited, the operation will be brief and it will reduce the terror risk to Turkey in the period ahead,” Simsek, who oversees economic affairs, said at a ceremony in Ankara.

A senior Turkish official declined to give a timeframe for the operation but said it would “move fast”, adding that Turkey believed there was some local support in both Afrin and Manbij for its action. “Some tribes are even offering to take part in the Manbij operation,” the official said.