President Obama on Friday authorized up to 1,500 more U.S. troops to join the training and advise-and-assist mission in Iraq against Islamic militants, the White House announced.

The new mission will greatly expand the geographical reach of the U.S. mission that until now has been limited to the Baghdad area and the Kurdish city of Irbil, and is aimed at pushing back into areas that had been overrun earlier this year by Islamic State militants.

"This is a change in geography. We are going to now put advisory teams out in what we consider to be expeditionary geography where the Iraqis are taking the fight to the enemy," Pentagon spokesman Rear Adm. John Kirby said Friday.

The mission in Iraq is authorized to have 1,600 troops assigned to it, although only 1,400 are in Iraq now. By the end of the year, that figure likely will rise to nearly 3,000. And for the first time in years, U.S troops will be operating in Anbar province — most likely out of Al Asad Air Base — in western Iraq, as well as from additional outposts in parts of northern Iraq.

The 1,500 new troops will be assigned to two primary missions.

One group of about 630 U.S. troops will expand the existing "advise-and-assist" effort working alongside Iraqi troops in headquarters units down to the brigade level. They will be working with 12 brigades, including nine Iraqi Army brigades and three Kurdish peshmerga brigades, a defense official said.

Their mission will be to help Iraqi commanders overseeing combat operations to "collate and process intelligence, help them develop operational enablers and assist them at the brigade or division level," a senior administration official said. This group of U.S. troops will include some Special Forces teams and also enablers for force protection, logistics and command-and-control functions, a defense official said.

Another group of roughly 870 troops will launch a new mission component: setting up and operating training centers for Iraqis in several locations outside Baghdad. Inside those facilities, U.S. troops will provide "old-fashioned training" for Iraqis, including combat drills, according to one defense official.

The American trainers eventually may provide training for Sunni irregular militias, which U.S officials say are a key part of the strategy to defeat the Islamic State, Kirby said.

"We're going to look at that," he said.

Kirby added that about 700 coalition troops are expected to join the training mission, including 120 soldiers from Denmark.

"Over the coming weeks, as we finalize the training site locations, the United States will work with coalition members to determine how many U.S. and coalition personnel will be required at each location for the training effort," Kirby said.

Building the capacity of local forces is a pillar in the U.S. strategy to counter the Islamic State, the White House said.

"We have been providing this support for Iraqi Security Forces through advise and assist programs; through the provision of weapons, equipment and intelligence; and through airstrikes with our coalition partners to enable our Iraqi partners' success," officials said in a statement.

Both White House and defense officials were careful to emphasize that American service members will not be conducting ground combat operations.

"It does not change the president policy that U.S. forces will not be engaged in combat," one senior administration official said Friday. "Even as these forces are able to deploy to different parts of the country to provide the train, advise and assist mission, they will not be introduced into combat."

The new troops would operate under the Army's 1st Infantry Division headquarters, which took command in theater Oct. 31. The deployments will take place "over the coming months," Kirby said.

It was unclear Friday which specific units will deploy to Iraq as part of this troop increase.

A former four-star commander told Military Times Friday that the U.S. training mission should focus the Iraqis on special operations with a goal of getting "eyes on the ground" on the Islamic State.

"We often talk about boots on the ground ... what we really need are eyes on the ground so that we can more accurately use air [power] against the Islamic State," said Adm. James Stavridis, chief of the U.S. European Command and Supreme Allied Commander Europe from 2009 to 2013.

While Stavridis applauded the move to send more troops to Iraq, he feels the U.S. still will not have enough advisers working with Iraqi security forces.

He said he believes the correct number is in "the range of 10,000."

"People don't want to hear that," said Stavridis, said Stavridis, dean of the Fletcher School of Law and Diplomacy at Tufts University. "We've all got 'Middle East fatigue.' But if we want to enable the Iraqi security forces to operate effectively, we're going to have to have sufficient number of advisers."

While the expanded mission will edge U.S. advisers closer to dangerous situations, they do not necessarily have to accompany Iraqi troops into combat, he said.

"The vast majority of the training and mentoring will be done from well away the front-line fighting," he said. "But some of the Special Forces operations will require front-line activities."

To pay for the expanded operations, Obama is asking Congress to approve a new $5.6 billion "Iraq Train and Equip fund," money above and beyond the $58.6 billion annual overseas contingency operations funding request submitted earlier this year, officials said.

Staff writer Jeff Schogol contributed to this report.