Turkish tanks, American warplanes and Syrian rebels joined forces Wednesday in a major cross-border assault into northern Syria that quickly pushed Islamic State forces from a strategic border town, officials from the U.S. and Turkey said.

The offensive marked the Turkish military’s biggest foray into the nearly 5½-year-old Syrian war as Ankara, with U.S. support, seeks to reshape the battlefield and put two adversaries on the defensive, officials said.

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