A steep temperature rise in the No. 2 reactor at Japan's crippled Fukushima nuclear power plant has sparked new concerns about government claims that the facility has been stabilized.

A magnitude-9 earthquake and tsunami l March 11 led to a meltdown at the plant.

The rise in temperature, first detected last Thursday, reached 73.3 degrees Celsius on Monday, an increase of more than 20 degrees Celsius, Kyodo News reports.

Tokyo Electric Power Co., operator of the plant, said the temperature had fallen to 68.5 degrees Celsius by early Tuesday evening.

The massive amounts of water injected into the reactor Tuesday to decrease the temperature was the highest level since the plant was said to have achieved cold shutdown in December.

"The temperature of the reactor pressure vessel seems to be close to peaking out," TEPCO spokesman Junichi Matsumoto told reporters Tuesday, referring to the 68.5 degree reading, Kyodo reports.

Last month, TEPCO changed pipes and the amount of coolant water in the reactor.

"This was a process to enhance stability but it has become clear that there is a possibility (the replacement work created) an unstable situation temporarily," said Goshi Hosono, state minister in charge of the Fukushima disaster. "We have to consider matters in an even more careful way."

While just five Japan's 54 nuclear reactors are currently online in the wake of the Fukushima disaster, all of the country's nuclear power plants are scheduled to be halted for servicing by the end of April.

Prior to the Fukushima disaster, nuclear energy accounted for 29 percent of Japan's electricity supply and the government aimed to increase that share to 41 percent by 2017 and 50 percent by 2030.

"If we can have a few [reactor] restarts, it will make things a bit easier -- but since we can't know if that will be possible, we have to prepare for the possibility that none are restarted," Japanese Trade Minister Yukio Edano recently told the Financial Times.

Meanwhile, the Japanese government is preparing a national energy plan that is likely to abandon swift development of nuclear power and instead place more emphasis on renewable energy.

"The handling of the continuing nuclear crisis has been problematic particularly due to the government's lack of readiness, which has generated suspicions that the disaster could have been mitigated had the government been more capable of crisis management," states an editorial in Japan's The Mainichi Daily News.