President Joe Biden said on Wednesday he will begin withdrawing U.S. troops from Afghanistan on May 1 to end America's longest war, rejecting calls for U.S. forces to stay to ensure a peaceful resolution to that nation's grinding internal conflict.

In a White House speech, Biden acknowledged that U.S. objectives in Afghanistan had become "increasingly unclear" over the past decade. He set a deadline for withdrawing all 2,500 U.S. troops remaining in Afghanistan by Sept. 11, exactly 20 years after al Qaeda's attacks on the United States that triggered the war.

But by pulling out without a clear victory, the United States opens itself to criticism that a withdrawal represents a de facto admission of failure for American military strategy.