(Adds IAEA quotes, background on outage)
VIENNA, March 20 (Reuters) - Japanese authorities say the cooling systems at all spent fuel pools at the Fukushima nuclear power plant have resumed operations after a power outage earlier this week, the U.N. atomic energy agency said on Wednesday.
Tokyo Electric Power Co had lost power used for cooling spent uranium fuel rods at its Fukushima Daiichi plant, illustrating the challenges the Japanese utility faces in trying to shut down the facility after meltdowns two years ago.
The company, also known as Tepco, said on Tuesday there was no immediate threat of overheating or radiation releases after the loss of electricity on Monday. It partially restored power by Tuesday afternoon, the company said.
But the power loss showed that the plant remained in a precarious state after an earthquake and tsunami in March 2011 damaged the plant, causing the world's worst nuclear accident in 25 years.
The Vienna-based IAEA said in a statement: "Japan's Nuclear Regulation Authority (NRA) has informed the International Atomic Energy Agency that cooling systems at all spent fuel pools at the Fukushima Daiichi Nuclear Power Station have resumed operation."
The power outage began on Monday, disabling spent fuel cooling systems at reactor units 1,3 and 4 as well as the common spent fuel pool, the IAEA said. The cooling systems at units 1, 3 and 4 were restarted on Tuesday local time and the common spent fuel pool shortly after midnight on Wednesday, it added.
"The operator...continues to investigate the cause of the power outage," the IAEA said.
Reporting by Fredrik Dahl; Editing by Angus MacSwan