Gen. Ray Odierno, former chief of staff of the Army, said Tuesday that the U.S. would likely have to put ground troops in Iraq and Syria in order to defeat the Islamic State, joining growing calls to put more boots on the ground in the Middle East.

"You can't defeat ISIS without having people on the ground," the retired general said on MSNBC's "Morning Joe." "The intelligence we're missing is the intelligence you gain on the ground. We need unit intelligence."

Odierno said he was "surprised" at the lack of conversation about a coalition to fight the Islamic State.

"The Kurds are only going to do so much," Odierno said of the regional group President Obama often cites as a key partner in the war against the Islamic State. "You need a plan that goes after Iraq, that goes after Syria."

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