The Pentagon said on Friday the military mission in Iraq and Syria would not change after the US intelligence community sharply raised its estimate of the number of Islamic State fighters in Iraq and Syria.According to intelligence sources, the estimate of the number of Islamic State fighters in Iraq and Syria is between 20,000 and 31,500. The previous estimate, in June, was about 10,000 fighters."The numbers certainly got bigger and that certainly intensifies the scope of the enemy that you're facing. I don't think there's a direct line between that and the duration of the conflict or the difficulty of the conflict. Believe me, everybody here at the Pentagon knows what we're up against and is taking it very seriously," Pentagon spokesman Rear Admiral John Kirby told reporters during a press briefing.