A top U.S. nuclear regulator indicated Thursday it is likely to take several weeks to cool down troubled nuclear reactors in Japan's northeastern prefecture of Fukushima.

''This is something that will take some time to work through, possibly weeks, as you eventually remove the majority of the heat from the reactors and then the spent fuel pools,'' U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko told a news conference at the White House.

While noting the situation of Tokyo Electric Power Co.'s Fukushima Daiichi Nuclear Power Station ''continues to be very dramatic,'' Jaczko declined to say whether Japan will avoid a worst-case scenario.

''I really don't want to speculate on where this could go,'' he said, adding that the United States will continue to provide Japan with necessary support to address the problem.

Japan is struggling to prevent high levels of radiation from emitting from the reactors that were hit by a powerful earthquake and tsunami a week ago.

==Kyodo