The Nuclear Regulatory Commission says it found a security-related problem at the Prairie Island nuclear plant that requires additional inspections.
The NRC said because the problem at Prairie Island is related to security it will release little information about what it found.
In a statement, Xcel Energy said security and safety are the company's highest priorities, and the company will decide within the next month whether to appeal the NRC finding.
Last October, an NRC inspection revealed an undisclosed issue that called for more attention. The agency said Xcel Energy "corrected or compensated for the deficiencies, and the plant was in compliance with requirements before the inspector left the site."
It's common for the Nuclear Regulatory Commission to withhold information about security at nuclear plants.
Prairie Island was subject to extra inspections until late in 2010, as it worked through a backlog of problems.