Amid an energy crisis sparked by a cut in Russian supplies, Berlin had already announced this month it would keep the plants on standby beyond the end of 2022 -- rather than shutting them down as originally planned.

But Economy Minister Robert Habeck said the situation in neighbouring France -- a key supplier -- was "not good, and had become considerably worse in recent weeks".

France's nuclear plants would be able to produce considerably less energy than originally expected, he added.

"If these forecasts do not turn around, then -- as the minister responsible for energy security -- I have to say today that (the two plants) will likely remain online in the first quarter of 2023," he said.

France, which has long relied on nuclear power, has itself been struggling after a number of its reactors were shut down due to corrosion issues.

The decision by Berlin not to turn off the installations -- affecting two of Germany's three remaining plants -- was a U-turn that delayed a nuclear exit planned under former chancellor Angela Merkel.

An initial stress test in March had found that the remaining nuclear fleet was not needed to ensure energy security, leading to the conclusion that they could be phased out by the year's end as originally planned.

But the electricity market has since been upended by Russia's invasion of Ukraine, with power bills soaring in part because Moscow cut energy supplies to Europe.

Habeck's initial announcement that the plants would be put on standby triggered a heated debate that exposed divisions within the ruling coalition.

Habeck's Green party, which has its roots in the anti-nuclear movement, faced pressure from the liberal FDP to keep all three plants running.

In an interview with T-online, Finance Minister Christian Lindner of the FDP made his demand clear, saying that "all three (nuclear plants) must stay on the grid so they can deliver electricity".

"That would reduce prices and prevent blackouts," he said.