(CNN)Several hundred US troops have left Afghanistan, on the same day President Joe Biden decided not to extend the August 31 evacuation deadline, Pentagon press secretary John Kirby confirmed Tuesday evening. "These troops represent a mix of headquarters staff, maintenance and other enabling functions that were scheduled to leave and whose mission at the airport was complete. Their departure represents prudent and efficient force management. It will have no impact on the mission at hand," Kirby said in a statement, confirming CNN's earlier reporting from two defense officials that the US' troop withdrawal from Afghanistan had kicked off. The fact...