The UN's atomic watchdog was Thursday monitoring Slovenia's only nuclear power plant following a leak in the cooling system that prompted an EU-wide radiation alert.
According to the Slovenian authorities there had been no radiation leak, the International Atomic Energy Agency said.
The Slovenian Nuclear Safety Administration (SNSA) had informed the IAEA's Incident and Emergency Centre about an "unusual event" at the Krsko nuclear power plant, said an IAEA statement released late Wednesday.
But the SNSA "said there was no radiation release to the environment."
Wednesday's incident had been at "the lowest level of emergency out of four levels as defined by the SNSA," the IAEA explained.
Acccording to the Slovenian authorities, plant operators had detected a loss in the reactor's cooling system at 3:07 pm (1307 GMT) "and decided to manually shut it down."
"SNSA said that the loss of coolant was detected in time and no radiation was released to the environment and there was no off-site impact," the statement added.
The SNSA had subsequently informed the IAEA that the reactor shut-down process was completed at 9:30 pm (1930 GMT).
At Slovenia's request, the IAEA Incident and Emergency Centre then informed the neighbouring countries Austria, Croatia, Hungary and Italy.
In Brussels, the European Commission issued an EU-wide radiation alert following the incident in the central European state that currently holds the European Union's rotating presidency.
Krsko, which is jointly owned by Slovenia and neighbouring Croatia, produces 20 percent of all electricity used in Slovenia and satisfies 15 percent of Croatia's power needs.