After a pre-dawn barrage of heavy artillery and airstrikes, Turkish tanks and special forces pushed into Syria on Wednesday in a U.S.-backed assault aiming to retake a border town from Islamic State militants and contain Kurdish expansion. It marked the NATO member's most significant military involvement so far in the Syria conflict.

The U.S. military has backed the operation with eight airstrikes, a senior defense official told Fox News. A second U.S. defense official said airstrikes were "still ongoing."

The unprecedented incursion marked a dangerous escalation in the Syrian conflict -- and demonstrates the twisted rivalries that run through the war. The U.S. has long pushed for more aggressive action by Turkey against ISIS. But Turkey's move to thwart Kurdish ambitions puts it on a path toward potential confrontation with Kurdish fighters in Syria who are also supported by the United States and have been the most effective force battling ISIS in northern Syria....