Fortum, which has proposed ringfencing Uniper's German businesses under government ownership, responded that it had already given Uniper 8 billion euros in loans and guarantees.

"The German security of supply businesses need to be owned by the federal state that has the required strong creditworthiness," since gas prices might continue to rise, said Fortum chief executive Markus Rauram in an emailed statement.

For Finland, its economy a 13th the size of Germany's and with a 15th the population, the challenge is serious.

"The rescue of Uniper is an issue of European importance." said Finnish Europe minister Tytti Tuppurainen, also in an email. "We are urgently calling for Uniper's at-risk, system-critical businesses to be ringfenced in Germany and secured by the state."

After prospering from years of dependable flows of cheap Russian gas, Germany is scrambling to contain the impact of those supplies being constrained.

While Russia blames technical problems, Western governments say these are pretexts and that Moscow is responding to crippling sanctions imposed over its invasion of Ukraine.

German has allocated 15 billion euros of public money to buy gas from elsewhere to ensure gas storages are full by the winter, but, urging the public to save energy, Habeck warned that if gas prices climbed further that might not be enough.

"Germans shower for an average of 10 minutes," he said. "And I think even five minutes is too long."

Already, some housing associations have said they will lowering heating temperatures in their houses and apartments this winter, and Habeck said workplace heating could be dialled down.

German Chancellor Olaf Scholz said in a video statement on Saturday that energy security questions would preoccupy Germany "for the coming weeks, months and years".