A 35-year-old nuclear plant in Slovenia was restarted Friday after it automatically shut down because of a water supply problem, its operator said.

"The unexpected malfunction was fixed... After thorough testing, the power plant was restarted and reconnected to the system," the Krsko nuclear plant said in a statement.

The facility in Krsko, some 100 kilometres (60 miles) east of the capital Ljubljana, shut down on Thursday because of anomalies in a valve regulating the water supply system.

There was no radiation danger during the incident, which came three months after a shutdown for regular maintenance work.

The 700-megawatt Westinghouse reactor was built in the former Yugoslavia and went into service in 1983.

It has been jointly run with neighbouring Croatia since the breakup of Yugoslavia.

The station was originally due to be switched off in 2023, but two years ago Ljubljana and Zagreb decided to extend its lifetime by another 20 years.

A decade ago, a cooling water leak at the plant triggered a Europe-wide alert procedure, the first since the Chernobyl catastrophe in 1986.

Several NGOs, including Greenpeace, have demanded the dismantling of the station close to Zagreb, because of its age and also because of earthquake risks in the region.

Krsko covers around 20 percent of Slovenia's electricity needs and 15 percent of those in Croatia.