For US in Syria, end game gets murkier as IS shrinks

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The closer the U.S. gets to its original goal in Syria of defeating the Islamic State group, the murkier its end game becomes.

New layers of complexity are descending on a shifting battlefield, as demonstrated by a deadly barrage of American air and artillery strikes on a shadowy attacker.

The Pentagon insists it is keeping its focus on defeating IS, but Defense Secretary Jim Mattis says U.S.-backed fighters in eastern Syria faced a "perplexing" overnight assault by about 300 pro-Syrian government fighters whose nationalities, motives and makeup he could not identify.

A number of U.S. military advisers were present alongside local allied forces, and the Americans led a punishing response that killed about 100 of the assailants.

Mattis says the incident doesn't portend a deeper involvement in Syria's civil war.