The European Commission has called for a full investigation into the causes of a blackout that left swathes of western Europe without power at the weekend.
The comments of Energy Commissioner Andris Piebalgs came after German electricity firm E.ON admitted that it was to blame for the power cut.
E.ON said its grid had overloaded after it temporarily switched off an electricity line in northern Germany.
Mr Piebalgs said the power cut was "unacceptable".
He added that Saturday's two-hour blackout once again showed the need for a Europe-wide common policy on electricity distribution.
"Energy security is better delivered through a common European approach rather than 27 different approaches," he said.
E.ON said the offending power line crossed over the river Ems and was turned off to allow a cruise ship to safely pass through.
The knock-on power cut left millions without electricity across Germany, France, Italy, Spain and Portugal.
Despite politicians' anger, E.ON said Europe's power grid was in good shape.
'Knock-on effect'
"I am grateful that the situation was not worse than it turned out, because E.ON caused it," said E.ON board member Klaus-Dieter Maubach.
"The trigger of the breakdown in supply was that we had to take a line out of operation and that the knock-on effect from that loss spread to other lines which later cut out."
Mr Maubach added that European grid operators enjoyed good co-operation, meaning Saturday night's power cuts only lasted for about an hour.
Yet politicians from the affected countries have called for the electricity companies to invest more in their networks.
"We have known for a while that there are bottlenecks on the power grids and that the utilities have not ensured that the grids are being expanded," said German Environment Minister Sigmar Gabriel.
Italy's prime minister has called for Europe to have a central power authority.
Romano Prodi said there was a "contradiction" in having a unified power network but no central authority.
Past examples
Saturday's power cut started in the German city of Cologne before quickly spreading.
Belgium, the Netherlands, Austria and Croatia were also affected, with the cuts even reaching as far as Morocco.
The worst recent power blackout struck Italy in 2003, plunging the country into darkness for 18 hours between 28 and 29 September.
The previous month, a similar power cut had struck the north-eastern US and Canada.
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