Germany's environment minister Barbara Hendricks said Monday she was reassured for the moment over the safety of Belgian nuclear power plants that have also worried the Netherlands and Luxembourg.

Hendricks was the latest European minister to hold talks with Belgian officials following similar meetings last month involving Luxembourg and the Netherlands about the ageing Doel and Tihange nuclear power plants.

"For now I am reassured. We will see," Hendricks said after talks with Belgian Interior Minister Jan Jambon.

"Belgium has assured us that experts will respond to the catalogue of questions from the German government in February," she added.

In March, she said, the two sides will hold an ad hoc working group of experts.

Jambon said each side would visit the other's plants to conduct inspections.

The concerns have largely emerged since the Belgian government's decision in December to extend the lives of 40-year-old reactors Doel 1 and Doel 2 until 2025 under a deal to preserve jobs and invest in the transition to cleaner energy.

It had originally shuttered Doel 1, the country's oldest reactor, in February 2015, but just three days after it was restarted in December it had to be closed due to a generator problem. It has now been restarted for a second time.

Tiny cracks discovered in 2012 in the reactor pressure vessels of Doel 3 and Tihange 2 also caused lengthy closures of those two reactors. They were both restarted at the end of last year, one having to close quickly again, for a few days, after a water leak.

And the Doel 4 reactor was also shut down urgently in August 2014 after a leak in the turbine hall, caused by tampering, gushed out 65,000 litres of oil lubricant. The investigation continues.

By 6:00 pm (1700 GMT), there were more than 770,000 signatures on a petition circulated by the activist group Avaaz, calling for a cross-border environmental impact study of all the Belgian nuclear reactors. The plants should be closed pending the conclusions of the study, Avaaz said.