TAMPA, Fla. (AP) -- President Barack Obama says U.S. forces in Iraq "do not and will not" have a combat mission as part of the effort against Islamic State militants.

Obama received a briefing Wednesday from officers at U.S. Central Command in Tampa, Florida. That command oversees military efforts in the Mideast.

The president says the fight against the Islamic State group cannot be America's alone and will require a broad coalition.

He says some nations will assist the U.S. with airstrikes and others will help train forces.

President Barack Obama, before the start of a briefing at MacDill Air Force Base, Fla. (AP Photo/Pablo Martinez Monsivais)

On Tuesday, the top U.S. military officer said American ground troops may be needed to battle the militants if Obama's current strategy fails.

Obama met with top officers at U.S. Central Command in Tampa, which oversees U.S. military efforts in the Middle East. Accompanying him were his national security adviser, Susan Rice, and Defense Secretary Chuck Hagel. Obama was to address Central Command troops, providing him another opportunity to make a case for the air strike campaign he wants to carry out against Islamic State.

Obama was spending two days away from Washington to meet with the generals and the scientists charged with carrying out missions against two distinct national security threats, both of which are costing lives and threatening regional stability. He then returns to Washington for a meeting Thursday with Ukrainian President Petro Poroshenko, drawing attention to ongoing tensions with Russia.

In three high-profile days, Obama is seeking to display resolve amid lingering questions about how quickly he has responded to crises and whether his deliberative approach has allowed military, diplomatic and public health hot spots to flare up.

His meeting with top U.S. commanders comes amid newly raised doubts about the ability of the United States to rely on Iraqi forces, Kurds and Syrian opposition fighters to carry out a ground fight against the Islamic State militants and whether U.S. troops might have to play a combat role.

It also comes as Congress prepared to vote on Obama's request for authority to equip and train Syrian opposition fighters whom the administration deems as moderates in the Syrian civil war.

Lawmakers in both parties have raised worries that the U.S. might be unable to find enough Syrian rebels who could be trusted to confront the Islamic State or that their numbers would be sufficient against the extremists.

"We must ... ask ourselves if we can truly `vet' these rebel groups beyond their known affiliations," said Rep. Peter Visclosky, D-Ind., "and ensure we are not arming the next extremist threat to the region and the world."

Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, raised new doubts about Iraq's role in the fight, telling a small group of reporters traveling with him to Paris that about half of Iraq's army is incapable of being an effective partner with the U.S. to push the Islamic State back in western and northern Iraq. He said the other half needs to be partially rebuilt with U.S. training and additional equipment.

Dempsey told senators Tuesday that if it became necessary for U.S. military advisers to accompany Iraqi troops into combat he might "go back to the president and make a recommendation that may include the use of ground forces."

The White House, however, remained firm about Obama's view. "What he's been very specific and precise about is that he will not deploy ground troops in a combat role into Iraq or Syria," White House spokesman Josh Earnest said in response to Dempsey's comments.

In Tampa, Obama was meeting with Gen. Lloyd Austin, who will oversee the military campaign against the Islamic State group as the head of Central Command, and other military officers to discuss operational details.

The day before, Obama announced the deployment of 3,000 U.S. troops to West Africa to help contain the Ebola outbreak that has already cost at least 2,400 lives and threatens to spread exponentially in the region.

While one is distinctly military and the other medical, Obama's challenges in the Middle East and Africa bear uncanny similarities. In both instances he has been accused of being slow to recognize a threat, and now he is responding with ramped-up efforts in both cases. He also has been pressured to offer reassurances that the primary terrorist and health threats rest abroad and that the risks to the United States are low.

In both cases he has issued a call for international action, warning that the threat of regional instability could spread. To confront the Islamic State militants, Obama has said he is relying on the U.S.'s military, its diplomats and its allies. Confronting Ebola on Tuesday, he had his national security team alongside top officials from the Centers for Disease Control and Prevention in Atlanta.

Declaring a "national security priority," he said: "We're working this across our entire government, which is why today I'm joined by leaders throughout my administration, including from my national security team."

It was about the fight against Ebola, but it could have been about the Islamic State threat just as well.

AP National Security Writer Robert Burns in Paris and Associated Press writer Andrew Taylor in Washington contributed to this report.

Reach Jim Kuhnhenn on Twitter at http://twitter.com/jkuhnhenn

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