Operator Tokyo Electric Power Co. has been under fire for failure to stop the flow of contaminated water from the plant crippled in the March 2011 earthquake and tsunami.
"This is not an issue where we can let Tepco take complete responsibility," CNN on Thursday quoted Prime Minister Shinzo Abe as saying from the government's nuclear disaster response headquarters. "We have to deal with this at a national level."
The prime minister said he has told Japan's Ministry of Trade and Industry to "provide multiple, speedy and sure solutions to this issue."
Abe's directive follows a government announcement Wednesday some 300 tons of groundwater containing radioactive waste could be flowing daily from the crippled nuclear complex into the adjacent Pacific Ocean.
To stop the radioactive water from leaking into the sea, Tepco has proposed a wall of frozen soil in front of the plant.
"To build such a wall, the government should take the lead to promote this kind of project," said Yoshihide Suga, Japan's chief Cabinet secretary. "We have to provide the support to do so."
The project to freeze the ground -- proposed by Japanese construction company Kajima -- involves drilling shafts into the nearly one-mile perimeter around the damaged reactors, then pouring in a chemical coolant.
"There's no blueprint, no nothing yet, so there's no way we can scrutinise it," Shinji Kinjo, who heads a task force set up by Nuclear Regulatory Authority to deal with the water issue, was quoted as saying by the Financial Times.
Ken Buesseler, a senior scientist at Woods Hole Oceanographic Institution in Massachusetts, in analyzing thousands of samples of fish from the Pacific near Fukushima, has found high levels of cesium-134, a radioactive substance, a report Wednesday on National Geographic's news website said.
"It's getting into the ocean, no doubt about it," he said. "The only news was that they finally admitted to this."
While the radioactive material leaked by the plant initially had a high concentration of cesium, the outflow into the ocean now is likely to be proportionally much higher in strontium-90, Buesseler said.
Although Buesseler is still not too concerned fish caught off the western coast of the United States will be affected, he noted that "strontium changes the equation for Japanese fisheries, as to when their fish will be safe to eat."
"Cesium is like salt -- it goes in and out of your body quickly," he said."Strontium gets into your bones."