U.S. Homeland Security Secretary Janet Napolitano says there are legitimate security concerns along the Canadian border that require tough new measures, and Canadians should realize that both sides will benefit.

But she would not comment on specific groups or individuals who may pose a concern, or whether suspected terrorists have been apprehended along the border without the public's knowledge.

"I think it is fair to say, and I think Canadian law enforcement would say, that there are individuals in Canada whose information is being shared with the United States and vice versa," Napolitano told CTV's Power Play on Wednesday.

During the interview, she repeatedly said that Canadians and U.S. citizens have a shared interest in border security.

"We know, for example, that we have some terrorist groups in the United States, and Canadians have an interest in being protected there, and likewise," she said at one point. "So we need to be working together to make sure we're sharing information."

She also touched on differences between immigration in Canada and the U.S., but would not say whether she felt those differences exposed a risk to the U.S.

"I don't want to say it that way in part because I have discovered Canada is very sensitive to that kind of implication," she said.

At an earlier press conference in Ottawa with Public Safety Minister Peter Van Loan, the two officials announced they had signed a number of new joint trade and security initiatives.

One of the programs is a joint assessment of threats to border security, while another would allow emergency vehicles, workers and equipment to cross the border more quickly in the event of an emergency.

The goal of both nations, Van Loan and Napolitano said, is to improve security and trade simultaneously -- saying one doesn't have to happen at the expense of the other.

But Napolitano, who cut her teeth as a politician in Arizona where problems along the Mexico-U.S. border is always a major issue, has come under criticism for seeming to focus on security over trade.

On March 25, she suggested the Mexican and Canadian borders should be treated the same.

Speaking on Power Play, Napolitano said there were obvious differences between the two borders, but U.S. law does not distinguish between the two.

"My job is to implement the law," she said. "But the techniques we use are going to be very different because the countries are very different and the challenges of the borders are very different."

But she added that contraband does enter the U.S. from Canada, and there is also illegal immigration -- although "the numbers are not the same as "Mexico" -- going both ways.

She also said she was taken aback by continuing criticism from Canadians after an embarrassing "misstatement," when she suggested some of the Sept. 11 terrorists entered the U.S. from Canada.

"In the United States, I've misspoken from time to time. I've been in elected office -- you immediately correct it, you apologize and move on," she said.

"What I regret is that Canada can't seem to get beyond one misstatement from what I'm trying to suggest. And what I am suggesting is that we share security concerns, just as we share trade concerns, and share all kinds of concerns. It behooves us both -- both nations -- to work together. We will, in the end, be stronger together."