Updated

More than three-quarters of Germany's nuclear power plants were offline Saturday due to maintenance work or shutdowns ordered by the government after Japan's Fukushima nuclear power plant disaster, utility companies said.

Only four of the country's 17 nuclear power plants were online after the energy utility RWE AG took its Emsland plant off the grid Saturday.

Environmentalists accused the utilities of staging simultaneous maintenance shutdowns while threatening blackouts to put pressure on Chancellor Angela Merkel's government, which appears determined in the wake of the Fukushima Dai-ichi catastrophe to phase out nuclear power within ten to 15 years. A decision on that policy is expected in June.

"We are afraid that the utilities could intentionally stage a blackout to influence people in the debate on phasing out nuclear power," said Jochen Stay of anti-nuclear group Ausgestrahlt.

A spokesman for RWE rejected the allegation, however, telling German news agency DAPD the maintenance at Emsland had been scheduled even before the disaster in Japan.

Experts said the situation was potentially worrisome, since a significantly lower electricity input could change the grid's overall voltage and in the worst case lead to blackouts.

"The situation will probably be manageable," the head of Germany's DENA electricity grid agency, Matthias Kurth, was quoted as saying in Saturday's Sueddeutsche Zeitung newspaper. "The situation would be worse if we didn't have that much sun at the moment" — a reference to the growing amount of electricity generated by solar panels across the country.

To compensate, Germany is likely to import more electricity from its neighbors, chiefly from France and the Czech Republic, which both rely heavily on nuclear power.

Germany, Europe's biggest economy, stands alone among the world's leading industrialized nations in its determination to ditch nuclear power and replace it with renewable energies. Nuclear power usually generates about 23 percent of Germany's electricity — about the same level as in the U.S. — but with the shutdowns it is now contributing less power than renewable energies, which normally provide 17 percent of Germany's power.

After the March 11 earthquake and tsunami crippled Japan's Fukushima plant, Merkel's government decided to shut down seven reactors built before 1980 pending thorough safety checks. Other plants have been taken off the grid in past weeks for scheduled maintenance.

Two reactors are scheduled to go back online by the end of next week, which should ease the tight domestic electricity supply.

Nuclear power has been very unpopular in Germany ever since radioactivity from the 1986 Chernobyl disaster drifted across the country.