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Former Secretary of State Madeleine Albright slammed Bernie Sanders on Saturday, expressing concerns over the Democratic presidential contender's "lack of knowledge" about foreign policy.

"We have to have a president that is ready on Day 1 to deal with problems," Albright told NBC News in an exclusive interview. "I have never seen such a complicated international situation, and we can't afford learning on the job."

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Albright, who has been stumping for fellow former Secretary of State Hillary Clinton in New Hampshire this weekend, added that Sanders' responses to foreign policy questions at the last presidential debate "surprised" her.

"I've been very concerned about his lack of knowledge," she said, citing his answer to a question about which country poses the biggest threat to the U.S. right now.

"I think that he gave very kind of simple answers," she said. "In contrast to Secretary Clinton, who not only talked about what was going on in each of those countries, but also [spoke about] the other concerns about it, and the relationship to each other, and what the United States had to look out for."

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Sanders has campaigned in part on the idea that he has better judgment on foreign policy than Clinton does — which Albright called a "strange statement," considering Clinton's own extensive experience as secretary of state from 2009 to 2013.

What is "so remarkable about Secretary Clinton is that she understands the relationship between domestic to foreign policy and vice-versa, and to the various, specific facts and how much she worked on it," Albright said.

"We have to have a president that is ready on Day 1 to deal with problems."

When asked whether Sanders' argument that he voted against the war in Iraq and Clinton voted for it shows he has a better track record on foreign policy, Albright called the vote a "very complicated issue."

"One vote is really not a strategy," she added.

Earlier Saturday, during a Clinton rally in Concord, New Hampshire, Albright defended Clinton's progressive and foreign policy credentials, and also made a plea to young women in the audience to vote for Clinton, arguing she is the best candidate to defend women's rights.

Related: What to Watch for in Saturday's New Hampshire GOP Debate

"Just remember, there's a special place in hell for women who don't help each other," Albright — who was the first-ever female secretary of state — told the audience, repeating a catchphrase she has become known for.

Albright, now a professor of international relations at Georgetown University and chair of Albright Stonebridge Group, a D.C.-based diplomacy firm, told NBC News that she felt that Sanders simply doesn't know enough about foreign issues to be president.

"One of my students just tweeted and said if he were in my class, I would tell him to rewrite the paper," she said.

According to an NBC News/Wall Street Journal/Marist New Hampshire Poll released earlier this week, Sanders leads Clinton by just 20 points days before Tuesday's New Hampshire primary.