The major u-turn in government policy was made after a second stress test to assess Germany's energy security as Russia reduces gas supplies to Europe.

Germany's three remaining nuclear plants were set to be retired at the end of the year. Instead, two of the fleet will be kept in reserve "until mid-April 2023 in case needed", Economy Minister Robert Habeck said on Monday.

But the decision has become a "stress test for the coalition" of Chancellor Olaf Scholz's Social Democrats, Habeck's Greens and the liberal FDP, according to the Sueddeutsche Zeitung daily.

Finance Minister Christian Lindner of the FDP has made no attempts to hide his push for the three plants to remain in use rather than just kept on standby.

"We shouldn't be too picky, but instead do everything that makes our lives easier," he told the Sueddeutsche Zeitung Monday ahead of the nuclear announcement.

That included "the continued operation of the nuclear power plants until at least 2024", the FDP boss said.

In a sign that he has not shifted his position, Lindner also retweeted several voices in his party criticising Monday evening's decision as not going far enough.

- 'Kept running' -

Habeck's decision partly delays the nuclear exit decided under former chancellor Angela Merkel after the Fukushima disaster in 2011.

He said the subject of nuclear energy was "bound with a lot of emotions" but that the partial extension was needed to avoid an "extremely unlikely" electricity crisis.

But in light of skyrocketing electricity bills, all possible resources needed to be mobilised, according to Veronika Grimm, a member of the government's council of economic advisors.

"That means not just coal plants but nuclear power plants too," she told daily FAZ on Tuesday.

"The plants should be kept running, not just be on standby, as is currently planned, because only then will it lower the price of electricity," she said.

The government should examine extending the lifetime of the plants by five years and even bringing recently closed plants back online to keep prices "within limits", she said.

By contrast, Claudia Kemfert of the economic research institute DIW pointed out that "nuclear plants are not adapted to act as network reserves because they cannot be fired up and shut down easily".

Meanwhile, the financial daily Handelsblatt wrote that the partial extension was simply "the worst of all possible decisions".

- 'Completely absurd' -

"We are heading towards an energy supply crisis," opposition CDU leader Friedrich Merz told German public radio.

Shutting down electricity generating capacity at a time of crisis was "completely absurd", he said, adding that the war-related crisis was being aggravated by "the decisions of the federal government".

Habeck had "ducked the risk of coming into conflict with a part of his party", Handelsblatt wrote.

The extension is a touchy issue for the Greens, which has its roots in Germany's anti-nuclear movement.

The decision was "hard to take but necessary as it stands", Green party chief Omid Nouripour told public television.

Habeck stressed Monday that Germany would not waver from its plan to move on from atomic energy.

"New fuel rods will not be put in," he said, adding that the issues this winter "cannot be compared" with the next one.

Habeck's ministry has chartered five floating terminals for the import of liquefied natural gas (LNG) to substitute for Russian supplies, the first of which are scheduled to come online at the end of the year.

At the same time, it has also moved to restart mothballed coal power plants and fill gas storage ahead of the winter to guard against an energy shortfall.