America's drumbeat back to war in Iraq grew stronger Monday, with the announcement the White House has approved raising the number of U.S. troops deployed there to more than 4,000. The U.S. will also deploy attack helicopters, rocket-powered artillery and hundreds of millions of dollars more to support Iraq's fight against the Islamic State group.

Defense Secretary Ash Carter announced in Baghdad on Monday that the limit on U.S. forces stationed in Iraq would be lifted by 217, raising the cap to 4,087. Pentagon officials could not say where these troops would come from or when they would arrive but said they would perform roles in advising and training, protecting U.S. forces, maintaining aircraft and calling in fire support.

These new forces could be drawn from the hundreds of additional U.S. personnel already in Iraq but not counted under the official limit the White House has set, such as the Marines firing artillery from Firebase Bell outside the Iraqi city of Makhmour, Pentagon officials said. The true number of Americans in Iraq, believed to exceed 5,000, includes troops on "temporary" duty, such as these Marines, or forces poised to replace others.

Perhaps most significantly are the new authorities offered to U.S. forces, which will now be able to embed at the battalion level of the Iraqi army to plan and support operations – potentially bringing U.S. advisers much closer to the front lines than before. Americans had previously been limited to advising division- and brigade-level headquarters – much larger military formations that kept U.S. forces away from combat, though occasionally near fighting, such as in the retaking of Ramadi.

"Clearly with coalition help, the [Iraqi security forces] have momentum, particularly as they move on to Mosul. To that end, we are looking to leverage strategic opportunities to support Iraqis' fight against ISIL," Pentagon spokesman Navy Capt. Jeff Davis said Monday, using an alternative name for the Islamic State group.

Carter also announced the U.S. had agreed to employ Apache attack helicopters in support of Iraqi forces as they move to retake Mosul. These powerful weapons had been available in the Iraqi army's retaking of Ramadi, but the government chose not to call on them. American High Mobility Artillery Rocket Systems, or HIMARS, the truck-mounted rocket launchers, will also be available to the Iraqis.

The new American support to the Iraqi central government – which the Pentagon says is based on a request from Baghdad – includes $415 million the U.S. expects Baghdad will pass on to the Kurdistan Regional Government, which oversees the highly effective but ethnically focused Kurdish peshmerga fighting units.

"They will help the KRG overcome severe impacts from its internal budget crisis through directed assistance to its peshmerga units involved in the counter-ISIL fight," Davis said. This will include stipends to fighters and other economic shortfalls, and will come from funds already allocated to fight the Islamic State group.