Turkey pushed ahead with a ground offensive against Kurdish forces in northwest Syria — in defiance of the United States — to create what it called a security buffer along the border.

Turkish soldiers moved into the town of Afrin Sunday morning, penetrating 3 miles from the Turkish border, NTV television reported, citing Prime Minister Binali Yildirim’s comments in Istanbul. Turkish F-16s and artillery units hit about 200 targets, the army said.

The incursion pits Turkey against a U.S.-backed force that played a crucial role in defeating Islamic State in Syria. Turkey considers the mostly Kurdish People’s Protection Units, known as YPG, to be a terrorist group linked to Kurdish separatists fighting government forces at home. Turkish military action also complicates Russian efforts to end the 7-year-old conflict in favor of Syria President Bashar Assad.

The U.S. is “very concerned” about the situation in northwest Syria, State Department spokeswoman Heather Nauert said in a statement. “We urge Turkey to show restraint and ensure its military operations remain limited in scope and duration and scrupulous to avoid civilian casualties.”

Turkey says it is invoking self-defense under international law, assuring Syria that the offensive was solely targeting “terrorists” and that its forces would withdraw after meeting its goals. French Foreign Minister Jean-Yves Le Drian called for an emergency United Nations Security Council meeting, drawing a rebuke from his Turkish counterpart Mevlut Cavusoglu on the grounds that such a move would amount to supporting for terrorism.

“We are determinedly taking steps against the terrorist organization and we will continue,” Turkish President Recep Tayyip Erdogan said in a speech Sunday in the western city of Bursa. “It is out of the question to make concessions on this.”

Five rockets believed to be fired by YPG forces from Syria exploded in the Turkish border town of Reyhanli, killing one person and wounding 32, local media said.
Turkey has been outraged by plans to include thousands of Kurdish fighters in a border security force being created by the U.S.-led coalition against Islamic State.

Territory won during Syria’s civil war has allowed the Kurds to carve out enclaves that they’d like to link through further conquests into a single contiguous region bordering Turkey’s southeast.

The incursion has also fueled tensions with Turkey’s Kurdish minority as Erdogan vowed to crack down on planned protests by the pro-Kurdish HDP party. U.S. officials, including Secretary of State Rex Tillerson, have denied that a Kurd-dominated border force is being created, though the coalition against Islamic State has confirmed it is being formed.

“Who are you deceiving?” Erdogan said. “We will eradicate all of them.”

The operation in Afrin will be followed by an offensive against Manbij, Erdogan said, referring to another Kurdish stronghold on the western bank of the Euphrates River, where some U.S. troops are deployed alongside Kurdish forces.

Erdogan said Turkey intended to finish the operation in a short time. Authorities declared areas bordering Afrin off-limits until Feb. 3. The plan is to create a buffer zone extending 18 miles into Syrian territory, Yildirim said, according to NTV. He played down any negative impact on the Turkish economy.