"Safety is our first priority," Leuthard said in a statement on Monday.
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 had expected to be made in mid-2012.
The Swiss Federal Nuclear Safety Inspectorate ENSI has been requested to do safety checks at the existing plants, the Swiss department of the environment, transport, energy and communications said in the statement.
Swiss utility companies Axpo, Alpiq (ALPH.S) and BKW (BKWN.S) said in December they would club together in their plans to build two new nuclear power to replace existing capacity.
(Reporting by Katie Reid)
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