U.S. President Barack Obama said on Thursday that he does not expect harmful radiation sparked by the crippled Japanese nuclear plant will reach the U.S., including its West Coast and Hawaii.

"We do not expect harmful levels of radiation to reach the United States, whether it's the West Coast, Hawaii, Alaska or U.S. territories in the Pacific," he said in a prepared speech at the White House.

Obama said right now the Centers for Disease Control and Prevention and public health experts do not recommend that people in the United States take precautionary measures beyond staying informed.

The damage to the nuclear reactors in Fukushima Daiichi plant poses a "substantial risk" to people nearby, said Obama, explaining the recommendation to evacuate U.S. citizens within 80- kilometer radius of the nuclear plant is based upon a "careful scientific evaluation."

He urged all U.S. citizens in Japan to carefully monitor the situation and follow the guidance of the U.S. and Japanese governments.

Obama said the Americans have seen the earthquake and tsunami render an unimaginable toll of death and destruction in Japan, and the powerful natural disaster caused even more catastrophe through its impact on the nuclear plant.

"The American people have been both heartbroken and deeply concerned about the developments in Japan," he said.

Obama said nuclear power is still an important part of the energy future of the U.S.

But the Americans have a "responsibility" to learn from this event and to draw from those lessons to ensure the safety and security of the nuclear plant, he added.

Obama said he has asked the Nuclear Regulatory Commission to do a "comprehensive review" of the safety of U.S. nuclear plants in light of the natural disaster that unfolded in Japan.

The 9-magnitude earthquake off Japan's coast on March 11 led to a release of radioactive materials from the Fukushima Daiichi nuclear power plant. The Japanese government is still struggling to cool the reactors and stored used nuclear fuel to avoid further release of radiation.