Story highlights Bernie Sanders says the United States and its allies needs to improve surveillance

He didn't offer specific steps to enhance surveillance in a Sunday morning interview

Washington (CNN) Vermont Sen. Bernie Sanders says the United States needs to toughen its surveillance to stop Brussels-style ISIS attacks, adding that "we know who ISIS is."

"It goes without saying that when you have attacks that take place, when 30 people get killed in Brussels, something went wrong ... We have got to improve our efforts to make sure it does not happen again," he told CNN's Jake Tapper on "State of the Union" Sunday when pressed for specifics.

Sanders credited President Barack Obama for his handling of the fight against ISIS, saying that the terrorist organization is "on the defensive. They are retreating."

Sanders also made a claim that seems at odds with intelligence agencies' concerns about ISIS-inspired attacks in Western countries.

"I think we know who ISIS is. We know those people who are planning attacks against our European allies and against ourselves," he said.

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