"The nuclear reactors at Fukushima Daiichi were badly damaged, have experienced a series of failures and pose serious hazard in the vicinity of the plant and a potential health hazard to a broader region," Under Secretary of State for Management Patrick Kennedy told reporters.
Noting that the US continuously supports the Japanese effort to respond to this nuclear emergency, Kennedy said the US is making available all available expertise, assets, equipments and technology at its disposal.
"Despite the best efforts of the responders, the situation remains very serious," Kennedy said and referred to the US recommendations to its citizens of evacuation within 50 miles radius of the damaged nuclear power plants. The continued release of radioactive material can't be rule out, he said.
Earlier, Chairman of the Nuclear Regulatory Commission (NRC) Gregory Jaczko told lawmakers at Congressional hearings that the situation of the Japanese nuclear plants was serious as the radiation level was high.
"We believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures," he said.
Fukushima Daiichi's unit 4 reactor appeared to have suffered a hydrogen explosion and that there "is no water in the spent-fuel pool, he said before the House Energy and Commerce Committee.
Jaczko said the high radiation levels might make it impossible to continue what he called the "backup backup" cooling functions that have so far helped check the fuel melting inside the reactors.
"Those efforts consist of using fire hoses to dump water on overheated fuel and then letting the radioactive steam vent into the atmosphere," he said.
Deputy Secretary of Energy Dan Poneman said the United States is watching the situation of these plants continuously.
"We are in consultation, comparing notes. IAEA is sending regular reports," he said.
In a late night travel alert, the Department of State warned its citizens of the deteriorating situation at the Fukushima Daiichi Nuclear Power Plant.
The United States Nuclear Regulatory Commission (NRC) recommends that US citizens who live within 50 miles of the Fukushima Daiichi Nuclear Power Plant evacuate the area or take shelter indoors if safe evacuation is not practical.
"The State Department strongly urges US citizens to defer travel to Japan at this time and those in Japan should consider departing," the travel alert said.
It also authorized the voluntary departure for family members and dependents of US government officials who wish to leave Northeast Japan.
Pentagon spokesman Col Dave Lapan said the US forces will remain in Japan and the US has full capability to fulfill its alliance commitments to defend Japan and maintain peace and security in the region.