This Jan. 11, 2000, file photo shows the Wolf Creek Nuclear power plant near New Strawn, Kan., which went online in 1985. (AP Photo/Capital Journal, David Eulitt, File)

Washington ? Three U.S. nuclear power plants need increased oversight from federal regulators because of safety problems or unplanned shutdowns, the Nuclear Regulatory Commission said Thursday, although officials said all are operating safely.

NRC Chairman Gregory Jaczko said the three plants — in South Carolina, Kansas and Nebraska — “are the plants we are most concerned about” among the 65 U.S. nuclear power plants in 31 states.

Jaczko did not identify the plants, but an agency spokesman said they are the H.B. Robinson nuclear plant in South Carolina, Fort Calhoun in Nebraska and Wolf Creek in Kansas.

An NRC spokesman said three reactors at the Oconee Nuclear Station in South Carolina had been on the watch list, but were removed two weeks ago after improved performance reviews.

The NRC stressed that all 104 U.S. nuclear reactors operate safely, and that the heightened review of the three plants was routine.

“The NRC felt the three required significant additional oversight but continue to operate safely,” said Scott Burnell, an agency spokesman.

All U.S. nuclear plants are inspected frequently. If enough minor problems or issues are identified, a plant moves to a second level of inspection, Burnell said.

Items that aren’t resolved in a reasonable time — or new items of higher significance — can move a plant to a third level of closer inspection and oversight. That is where the three plants in South Carolina, Kansas and Nebraska are listed, Burnell said.

The agency has two higher levels of concern for even more serious problems: one where senior NRC management becomes involved and a final level where a plant is shut down until officials determine it is safe to reopen. No U.S. plants are currently listed in either category.

Jaczko told a House energy panel the NRC has very strong safety program. The panel was meeting to review the agency’s budget and safety concerns in the wake of the nuclear crisis in Japan.

Rep. Ed Pastor, D-Ariz., said he was not worried about the NRC’s safety program.

“What about the condition of the reactors?” he asked. “Are they safe enough?”

Jaczko said that “right now, we have very good performance from the actual reactors,” but then said there were six reactors in need of more intensive review.

“Those are the plants we are most concerned about,” he said. “With the exception of those six plants, the remaining plants are operating with safety margins, and again all of the plants are meeting our safety requirements.”

Burnell and other agency officials said the six reactors Jaczko referred to included three at Oconee, which were recently taken off the watch list.

Nine of the 104 U.S. reactors are listed in the second, minor level of concern, Burnell said.