Leon Panetta
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Leon Panetta: Few foresaw IS threat to Iraq

Leon Panetta has told the BBC the situation with Islamic State [IS] militants in Iraq and Syria deteriorated faster than he had anticipated.

"I didn't believe that the Sunnis would be as discouraged as they are, and that some of that resulted in some of these foreign fighters going into Syria and becoming part of [IS]," he said.

"I think it's fair to say that although we knew that there were extremists in Syria, that there are very few that kind of looked at [IS] as that larger threat that it became, in terms of invading Iraq."

The former US defence secretary and CIA director told the BBC's Katty Kay in Washington that a "vacuum was created" in Iraq when US troops withdrew in 2011, and that the US government should have put more pressure on former Iraqi Prime Minister Nouri al-Maliki to allow US troops to remain.

He says it will take a "very long and sustained effort" to defeat IS.

Mr Panetta spoke to the BBC while promoting his book Worthy Fights.