BERLIN (AP) — Germany says it wants France to shut down its oldest nuclear plant as soon as possible amid reports Friday that an incident at the facility two years ago was more serious than previously known.

German daily Sueddeutsche Zeitung and public broadcaster WDR reported a series of problems when engineers tried to tackle a minor water leak that ended with an emergency shutdown of one of the two reactors at the Fessenheim plant, which lies just across the Rhine that marks the border between France and Germany.

The reports cite a letter from the French Nuclear Safety Authority to the head of the nuclear plant detailing the incident on April 9, 2014.

"It's not the first incident or the first problem that we know about from this reactor, and that's why the environment minister demands the reactor be shut down as soon as possible," said Stephan Haufe, a spokesman for Germany's environment ministry.

Haufe said the incident was discussed by a Franco-German nuclear safety panel at the time, and Berlin agreed with Paris' assessment about the seriousness of the incident — "one" on a scale from zero to seven.

Still, Germany was concerned about the age of the reactor, he said. "Such an old reactor, it was put into operation in 1977, of course has many technical problems. This is the case with several reactors on the German border." Germany has expressed concern about nuclear plants in Belgium and Switzerland in recent years.

The French Nuclear Safety Authority said Friday the 2014 incident was minor and was neither minimized nor hidden. The nuclear plant has been certified to function for another decade, it said.

The French government said last year it would close the plant no later than 2018 as part of a plan to reduce dependency on nuclear power.

Haufe said Germany has received mixed messages from Paris about the shutdown, with one response being that it wouldn't happen until a new plant goes online.

"We don't have really reliable information when this nuclear plant will be shut down," he said.

Following the Fukushima nuclear disaster in Japan, the German government decided in 2011 to switch off all its nuclear plants by 2022.