Instruments for the measurement of nuclear radiation to send to Swiss Rescue workers in Japan, are pictured at the Swiss Agency for Development and Cooperation (DEZA) logistic - centre in Wabern March 14, 2011. A magnitude 8.9 earthquake and tsunami which struck northern Japan on Friday. [Photo/Agencies]

ZURICH,- Switzerland has suspended the approvals process for three new nuclear power stations so safety standards can be revisited after the explosion at a Japanese plant, Energy Minister Doris Leuthard said on Monday.

"Safety is our first priority," Leuthard said in a statement.

Switzerland's five existing nuclear reactors generate about 40 percent of the country's electricity but some will have to be retired in coming years. Decisions on sites for new plants were due to be made in mid-2012.

Sites at Niederamt, Beznau and Muehleberg have been declared suitable and further feasibility studies are under way.

The Swiss ministry of the environment, transport, energy and communications (UVEK) said it was monitoring the situation in Japan and safety checks were being made at an existing plant at Muehleberg.

A Swiss Agency for Development and Cooperation (DEZA) worker packs instruments for the measurement of nuclear radiation to send to Swiss Rescue workers in Japan, at the DEZA logistic - center in Wabern March 14, 2011.[Photo/Agencies]

German Foreign Minister Guido Westerwelle said on Monday that a government decision to extend the life of Germany's nuclear power stations could be suspended.

The Swiss Federal Nuclear Safety Inspectorate (ENSI) has been requested to do safety checks at the existing plants, the ministry said in the statement.

ENSI has also been asked to analyse the causes of the accident in Japan and draw possible new and tighter safety standards, especially as far as safety is concerned in the case of an earthquake and in terms of cooling, the ministry said.

Swiss utility companies Axpo, Alpiq and BKW are among the companies interested in building new nuclear power plants in Switzerland.

In 1990, Swiss voters backed a 10-year moratorium on the building of nuclear power plants but they rejected extending the freeze in 2003, opening the way for the government to consider new plants to replace those that need retiring.

Last month, Swiss voters narrowly approved the building of a new plant in Muehleberg to replace the old one there, 20 percent owned by Germany's E.ON.