President Obama will dispatch more than 17,000 troops to Afghanistan, the White House announced Tuesday.

"This reinforcement will contribute to the security of the Afghan people and to stability in Afghanistan," Obama said in a statement. "I recognize the extraordinary strain that this deployment places on our troops and military families. I honor their service, and will give them the support they need."

Obama said the deteriorating security in Afghanistan made the troop increase necessary, adding that the country has not received the strategic attention or resources it needs.

Although 17,000 troops have been authorized to go, the Pentagon identified and mobilized only about 12,000. Of those troops, 8,000 will be Marines and the 4,000 others will comprise an Army Stryker Brigade.The additional 5,000 troops will be identified and announced at a later date.

But sources provided FOX News with the identity of all 17,000 troops: 10,000 will be Marines stationed in the South; 3,800 with an Army Stryker Brigade; 1,000 Special Operations Force trainers and 3,200 force enablers.

Obama also said he is withdrawing some U.S. troops from Iraq. He said that will give the Pentagon more flexibility in shifting troops to Afghanistan.

The troop increase is a down payment on a larger influx of U.S. forces that has been widely expected this year. It will get a few thousand forces in place in time for the increase in fighting that usually comes with warmer weather and ahead of national midyear elections.

A spokesman for Gen. David McKiernan told FOX News that they had already started to build camp barracks for the troops in anticipation of the announcement -- knowing how sensitive the timing is given the spring fighting season.

It is generally takes about three months for an Army brigade to deploy to the combat zone.

This is the first time the new commander in chief has sent significant numbers of new forces into battle. Obama campaigned on a new strategy for the Afghanistan war, but he has taken his time to approve the new forces. 

FOX News' Jennifer Griffin and Justin Fishel  and The Associated Press contributed to this report.