WASHINGTON – America’s top military officer said Friday up to 15,000 moderate Syrian rebels would be needed to dislodge Islamic State militants from their strongholds in northern and eastern Syria.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, made the assessment to reporters a week after Congress approved a plan to begin training and equipping 5,000 moderate Syrian rebels to take on the Islamic State, which has seized about a third of the territory in Syria and neighboring Iraq.

“Five thousand has never been the end state,” Dempsey said. “Twelve to 15,000 is what we believe they would need to recapture lost territory in eastern Syria” that the Islamic State controls.

Earlier this week, the U.S. and several Arab allies began bombing Syria, striking terrorist training compounds, headquarters and command and control facilities, storage facilities, a finance center, supply trucks, armed vehicles, and oil refineries. But Dempsey said that won’t be enough to defeat the Islamic State.

“There’s no airpower alone solution to ISIL either in Iraq or in Syria,” Dempsey said, using an acronym to refer to the Islamic State. “There has to be a ground component to the campaign against ISIL in Syria, and we believe that the path to develop that is the Syrian moderate opposition.”

At present, the moderate rebels are outmatched by their extremist counterparts.

“You’re really talking about a qualitative difference where these Islamist groups… have benefited from massive cash flows [and] from the defection of other fighters,” said Fredric Wehrey, a Middle East expert with the Carnegie Endowment for International Peace. “The opposition is still in a very beleaguered state.”

Dempsey believes it will be a long time before the rebels can become an effective fighting force, even with American training.

“We have to do it right, not fast. They have to have military leaders that bind them together. They have to be have a political structure into which they can hook and therefore be responsive to. And that’s going to take some time,” he said.

The lack of leadership among the rebels presents a real challenge to U.S. officials who want to build a large rebel fighting force.

“We don’t have a head of it,” Secretary of Defense Chuck Hagel told reporters at the press conference when asked who would lead the people that the U.S. trains. “As they will build their coalitions with our help, we’re not going to instruct them as to who their leaders are.”

Jeffrey White, a defense analyst at the Washington Institute for Near East Policy, described the rebel groups in Syria as “amorphous.”

“The people move back and forth. They’re constantly forming new alliances,” he said.

He noted that the moderate rebels and the extremists sometimes cooperate with each other when they fight against the Assad government, their mutual enemy in an ongoing civil war.

White, who supports the idea of training the moderate rebels, said there are inevitable risks in doing so.

“The commanders could change, the people could be bribed or suborned by other organizations to move over to them and bring their [American] training and weapons and so on,” he explained. “They’re going to change loyalties – some of them.”

He also suggested that they won’t necessarily live up to Western standards of military professionalism.

“You know they’re going to do bad things. Some of them are going to act like criminals. There might be an atrocity here or there. They’re not going to be under full military discipline,” he said. “If you deal with irregulars you’re going to have to expect to have these kinds of problems.” Twitter: @JHarperStripes

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