Meanwhile officials from Austria, Italy and Hungary said they had been informed that the coolant leak at the Krsko plant was only an exercise, while the rest of Europe had been told of the actual proportions of the event, Slovenian Environment Minister Janez Podobnik said Thursday.

After officials at Krsko Nuclear Power Plant reported that they had experienced possible problems with the reactor’s primary coolant system during a shutdown, all 27 members of the European Union were alerted by the European Commission.

But there was an apparent break down in communication with Slovenia’s immediate neighbours and Austria was particularly infuriated.

Podobnik told reporters in Luxembourg, where he was headed for a meeting of European environmental ministers, that Slovenia’s initial dispatch erroneously identified the events at the Krsko plant as an “exercise,” according to Agency France Presse.

"It used the wrong form. It used a form that had ‘exercise’ on it. It was a mistake that was a genuine human error," Podobnik said.

The International Atomic Energy Agency, which is currently monitoring the situation at Krsko, reported that it immediately notified Slovenia’s neighbours of Italy, Austria, Hungary, Italy and Croatia.

But the immediate Slovenian warning was not clarified before the Slovenians alerted the European Commission, using the correct form, which resulted in an EU-wide alert – a mistake that left Austria, Croatia and Hungary in the dark for some hours.

After the European Commission received word from Slovenia, it activated the European Community Urgent Radiological Information Exchange (ECURIE) system, immediately transmitting the information to all 27 member nations.

The system was introduced in 1987 after the Chernobyl disaster provide early notification and information exchange in the event of a radiological or nuclear emergency. Wednesday was the first time the alert system had been uses, said EU energy spokesman Ferran Tarradellas Espuny, AFP reported.

"It’s not okay to set off an alarm in Europe and inform Austria, Italy and Hungary that it’s only an exercise," Austrian Environment Minister Josef Proell told AFP.

"This has to be immediately clarified, and we want to know how this contradictory information came about," he said.

"The Austrian authorities have conducted tests at the border but they have not detected any increased radioactivity," he added, insisting: "There is no absolute security when it comes to nuclear power."

Croatia, however, was apparently lagging even further behind the information curve, and heard nothing of the possibly dangerous incident until, at the earliest, Austrian officials knew the true state of affairs.

Pavle Kalinic, the head of Croatian Emergencies Bureau, told Bellona Web that “friends from Austria” had informed him of the incident in the Krsko plant, which he described as "a permanent threat to Zagreb."

Krsko’s 696-megawatt light-water reactor, which was built by the US firm Westinghouse between 1974 and 1984, was the subject of disputed ownership between Slovenia and Croatia after the breakup of Yugoslavia. The plant produces 20 percent of all electricity used in Slovenia and satisfies 15 percent of Croatia’s power needs.

The two governments decided in 2002 to share the plant, which is located 30 kilometres from Zagreb, after a decade negotiations, which, according to Kalinic, “makes the late notification (about the incident) all the more insulting.”

According to the Slovenian authorities, plant operators had detected a loss in the reactor’s cooling system at 3:07 p.m. local time and manually shut it down.

The Slovenian Nuclear Safety Administration (SNSA) informed the IAEA’s Incident and Emergency Centre about an "unusual event" at Krsko, said an IAEA statement released late Wednesday.

The IAEA said the SNSA reported that there was no release of radiation into the environment, nor were any plant workers exposed.

This was corroborated by the European Commission dispatch to EU member States. The plant is taking safety measures, and, so far no contamination of the surrounding environment or of any of the plant workers has been observed, said the EU release.

Podobnik reaffirmed this in Luxembourg, saying “"Only a very minor repair is needed in a few days to come."

But Croatian officials report that while countries as far away as France and Germany has already been briefed on considering countermeasures to possible contamination, they were still operating in a media blackout, the Earth Times reported Zagreb media as saying.

Most Croatian media fixed at least part of the blame on the Croatian national electrical utility for keeping the incidents under wraps. "The national electric company HEP kept the incident secret more than three hours," one radio broadcast reported.

But most of Croatia’s ire came down on the SNSA.

Krsko’s chief executive, Stane Rozman, told Slovenian radio Thursday morning that the incident was not unusual for a nuclear power plant, and that the shutdown was standard procedure, according to the Earth Times.

He however refused to comment on the handling of the incident by the national nuclear authorities.

The Luxembourg gathering of environmental ministers, however, are not willing to let it go at that, and focused on the confusing information that Slovenia was apparently issuing to different countries..

"We will certainly have to ask: ‘Why did you do it?’" said German Environment Minister Sigmar Gabriel, even though he conceded: "I prefer to have an unnecessary alert, than to have too few alerts."