(CBS/AP) Japanese nuclear regulators discovered a fresh leak of radioactive material Thursday from an atomic energy plant damaged in an earthquake this week, a report said, adding to criticism of the embattled plant operator.

Nuclear inspectors probed the Kashiwazaki-Kariwa plant, which suffered a barrage of leaks and malfunctions in Monday's 6.8-magnitude quake in northwestern Japan. The plant was ordered shut down indefinitely on Wednesday.

Kyodo News agency said officials from the Nuclear and Industrial Safety Agency found radioactive iodine had leaked from an exhaust pipe at the plant. Operator Tokyo Electric Power Co. had already announced the release of other radioactive materials from the exhaust vent previously.

The inspectors concluded the leak was too small to harm the environment or public health, Kyodo reported. Officials at the agency said they could not immediately confirm the report.

Members of a separate panel, the Nuclear Safety Commission, also toured the plant on Thursday and regaled TEPCO for missteps in its response to Monday's quake, which killed at least 10 people and injured more than 1,000 others.

Still, the commission concluded none of the errors threatened public health.

"The safety of ... (the) plant was fundamentally maintained and we avoided the serious consequences of a nuclear accident," Commission Chairman Atsuyuki Suzuki said in a statement. "The list of problems announced by TEPCO have no serious effect on the safety of the reactor."

CBS News correspondent Steve Futterman reports that the contoversy surrounding the Japanese nuclear plant is lending strength to the argument against nuclear energy in another quake-prone area; California. Click here to listen to his report.

Commission members criticized TEPCO for a bungled response to a quake-triggered fire at an electrical transformer. Plant officials said they had no chemical fire vehicle at the plant, and local fire officials took 90 minutes to respond to their call.

The commission also said the fuel rods in the plant were stable, but that the inside of the reactors should be checked more thoroughly.

Chief Cabinet Secretary Yasuhisa Shiozaki on Thursday urged the operators of Japan's 55 nuclear reactors to speed up safety checks for earthquake-resistance, a top concern in this temblor-prone nation.

"Since there was such a huge earthquake that surpassed our expectations, we need to consider future measures for quake resistance," Shiozaki said. "I asked them to speed up the assessment and check ups wherever possible."

Meanwhile, the Japanese meteorological agency is reporting that a new analysis shows that a fault line may extend directly underneath the Kashiwazaki-Kariwa plant, reported CBS News' Celia Hatton. Power plant officials admit the facility was only designed to withstand an earthquake measuring 6.5 in magnitude. Monday night's earthquake was 6.8.

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