Turkey on Sunday continued a major attack inside northwestern Syria on a Kurdish militia it has called a "terror army" that presents a danger to Turkish security.

One day earlier Turkey sent tanks and armored vehicles lumbering across the border with Syria to add to artillery and aerial invasions already underway against the YPG, which Ankara seeks to drive out of the Afrin region of Syria.

Turkey also announced Saturday that the aerial component of its "Operation Olive Branch" had struck 108 YPG targets, as NPR's Peter Kenyon tells our newscast unit.

Turkey's incursion may heighten tensions with the United States, with which it has partnered but also quarreled.

The U.S. has repeatedly armed and trained the YPG, which it sees as a vital partner in its fight against ISIS. Ankara, however, sees the YPG as terrorists and too closely allied with another Kurdish militia, the PKK, which has operated inside Turkey for more than three decades. Both the United States and Turkey consider the PKK a terrorist group.

The Pentagon says it limits its assistance to the YPG to regions where ISIS is nearby. A U.S. general says he hopes Turkey's operation comes to a swift conclusion and that Ankara returns its focus to turning back ISIS, according to NPR's Kenyon.

For its part, the YPG claims it has handily countered Operation Olive Branch. "All the Turkish military's ground attacks against Afrin have been repelled so far and they have been forced to retreat," says YPG official Nouri Mahmoudi, according to Reuters.

The YPG appears to have launched its own counterattack within Turkey's borders as well. Turkish officials say rockets coming out of Syria killed one and injured 32 in the border town of Reyhanli. An earlier rocket attack on a different Turkish town reportedly inflicted no casualties.

Egypt and Iran have condemned Turkey's attack. Russia has urged restraint.

The Afrin region under assault by Turkish forces is home to at least 800,000 civilians, including refugees from the Syrian civil war, according to the Associated Press.

The wire service also reports that although Syria's government earlier claimed it would open fire on Turkish jets, on Sunday President Bashar Assad merely denounced Operation Olive Branch as "brutal aggression" and did not repeat his military threat.

Turkey's President Recep Tayyip Erdogan claimed his operation would be completed "in a very short time."

In November, Turkey claimed the Trump administration had agreed to no longer arm the YPG, as NPR's Maggie Penman reported. The White House did not confirm Turkey's account of an agreement, but did mention "pending adjustments to the military support provided to our partners on the ground in Syria." The news was a shock, given that in May the White House had spurned the idea of discontinuing support for the YPG.

Turkey's current assault on the U.S.-partnered YPG follows a year in which the relationship between the two NATO allies strained even further, with the Department of Justice refusing to assist in extraditing a cleric Erdogan claims sparked a failed coup attempt in 2016.

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