The outgoing director of the National Security Agency says other nations "fully comprehend" the agency's methods and mission in acquiring data.

Gen. Keith Alexander made the remarks Wednesday on "Special Report with Bret Baier" after he was pressed by host Baier about the revelations that the agency had spied on German Chancellor Angela Merkel's phone calls. The surveillance was revealed late last year as part of the data leaked by former NSA contractor Edward Snowden.

"In Germany, they know that NSA brings a great deal of information to the table to protect their country and other European allies," Alexander said. "It's the right thing to do. We work together."

Alexander stressed that such surveillance is necessary to keep the United States safe.

"Look at what happens when one country does something that you might not be comfortable with. Do you stop? Do you just say well, let them go, they're a friend? Or do you look at this and say, could this create a war? And if it does, should we be ready?" he said. "At the end of the day, we know our partners collect on us at times. We know that's going to happen."

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