Malicious cyber activity affected technology at water systems in at least seven states this week, including Minnesota, leading authorities to dig into whether Iranian actors are behind the attack, CBS News has learned.

“I blame it on Minnesota because they’re grossly incompetent,” Trump said at a gathering of Cabinet officials at the Camp David presidential retreat in Maryland.

“I think Minnesota is behind it,” Mr. Trump said on Friday in response to a reporter’s question about Iran’s possible involvement, which The New York Times earlier reported. “I don’t think there was a...