The U.S. defense chief is in Afghanistan, where he's getting a firsthand update on the conflict there.

FOX's Rachel Sutherland reports from Washington:

Defense Secretary James Mattis went to Kabul as the administration continues to assess the nation's longest war. Speaking to reporters, General Mattis said the military is under no illusions about the challenges associated with the mission:

(Mattis) "2017 is going to be another tough year for the valiant Afghan security forces and the international troops."

The visit came three days after the Taliban attacked a mosque on an Army base, killing at least 100 people. Secretary Mattis said it was a heinous attack, but also said it the Taliban is welcome to join the political process as long as it renounces violence and terror.

In Washington, Rachel Sutherland, FOX News.

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