Japan's trade ministry has ordered nuclear power plant operators to immediately start implementing new safety measures in light of the crisis at the Fukushima plant.
The ministry said the crisis was due to a higher tsunami than expected after the 9.0-magnitude earthquake on 11 March, which killed more than 27,500.
The steps, to be completed by the end of April, include preparing backup power in case of loss of power supply.
The plants will need to have fire trucks with hoses ready at all times to intervene and ensure cooling systems for both reactors and pools of used fuel are maintained.
The operators must also revise their own operating manuals and train staff based on the revised rules.
Minister of Economy, Trade and Industry Banri Kaieda said the measures, to be implemented by the ministry's safety agency, do not necessarily require nuclear plant operations to be halted.
'These are the minimum steps we can think of right now that should be done immediately,' Mr Kaieda said.
'We shouldn't wait until a so-called overhaul or a comprehensive revision - something major that would take a long time - is prepared. We should do whatever we can if and when there is something (which safety authorities agree is) viable and necessary,' he said.
The reactors at the Fukushima Daiichi plant automatically shut after the quake and subsequent tsunami devastated coastal areas of northeast Japan.
The crisis at the Fukushima plant of radiation leaks and partial meltdown of nuclear fuel had three direct causes, the ministry's Nuclear and Industrial Safety Agency said.
It pointed to a loss of emergency power and disabled cooling systems for reactors as well as for pools holding spent nuclear fuel.
Before the disaster, Japan's 55 nuclear reactors had provided about 30% of the nation's electric power.
The percentage had been expected to rise to 50% by 2030, which would be among the highest in the world.
The ministry added that Japan should start reconsidering its energy policy with a focus on the potential of solar power.
New readings showed a spike in radioactive iodine in the sea off the plant to 3,355 times the legal limit, the state nuclear safety agency said.
However, it played down the impact, saying people had left the area and fishing had stopped.
Pollution of the ocean is a concern for a country where fish is central to the diet.
Experts say the vastness of the ocean and a powerful current should dilute high levels of radiation, limiting the danger of contamination to fish and other marine life.
