Iraqi Shiite militia fighters hold the Islamic State flag as they celebrate after breaking the siege of Amerli by Islamic State militants, September 1, 2014. REUTERS/Youssef Boudlal The Defense Department is considering recommending the US send ground troops into Syria to fight the terrorist group ISIS, according to a source who spoke to CNN.

"It's possible that you may see conventional forces hit the ground in Syria for some period of time," a defense official told CNN.

There are currently hundreds of US troops in Syria offering training and assistance to US-backed local forces there. But conventional forces would likely be on the ground in larger numbers, according to CNN.

CNN reported last month that Defense Secretary Jim Mattis was taking control of a Pentagon review to determine which options the Defense Department would present to President Donald Trump on the fight against ISIS.

The defense official CNN cites in Wednesday's report stressed that any decision on Syria would ultimately be up to Trump.

Charles Lister, a senior fellow at the Middle East Institute and an expert on Syria, said he's "not surprised" to see that the US is considering ground troops in Syria to fight ISIS.

"Fits Trump desire for a rapid victory + withdrawal," he tweeted.