By Patricia Zengerle and David Morgan
WASHINGTON (Reuters) - President Barack Obama sent condolences to the people of Japan on Friday and said the United States would provide any help its close ally needed after a massive earthquake and tsunami killed hundreds.
The Defense Department was preparing American forces in the Pacific Ocean to provide relief after the quake, which generated a tsunami that headed across the Pacific past Hawaii and toward the west coast of the U.S. mainland.
Authorities said hundreds of people were killed in Japan and the toll was expected to surpass 1,000.
Obama was awakened by his chief of staff, Bill Daley, at about 4 a.m. EST and called Japanese Prime Minister Naoto Kan later in the morning.
"On behalf of the American people, I conveyed our deepest condolences, especially to the victims and their families, and I offered our Japanese friends whatever assistance is needed," Obama said at a midday news conference.
"I'm heartbroken by this tragedy," Obama said.
"The Japanese people are such close friends of ours," he added. "That just makes our concerns that much more acute."
Obama said Kan told him that so far there were no signs of a radiation leak at a nuclear plant hit by the quake.
Earlier, U.S. Secretary of State Hillary Clinton had said U.S. Air Force "assets" in Japan had delivered coolant to a nuclear plant. However, a U.S. official said Japan had asked the United States for the coolant, but ultimately handled the matter on its own.
Nuclear expert Edwin Lyman from the Union of Concerned Scientists told Reuters that although he did not have full information about what had happened at Tokyo Electric Power Co's nuclear plant in Fukushima, "every indication is that the type of event that has occurred there is one of the most serious things that can happen in a nuclear reactor."
He said that in the worst case, inability to cool the radioactive core would cause it to melt down, and escape into a containment building that is the last barrier to having radiation escape into the atmosphere.
"Then it's a dice roll whether or not the containment will retain its integrity and prevent a large radiological release," said Lyman.
Defense Secretary Robert Gates told reporters traveling with him in Bahrain that U.S. troops and military facilities in Japan were in good shape and willing to help.
"It's obviously a very sophisticated country but this is a huge disaster and we will do all, anything we are asked to do to help out," he said.
The military effort included at least six Navy ships, Pentagon spokeswoman Navy Commander Leslie Hullryde said.
The State Department said embassy operations in Japan were moved from Tokyo to another location as a precaution.
There have been no reports of Americans killed or injured in the quake. A State Department travel alert strongly urged Americans to avoid nonessential travel to Japan.
"Strong aftershocks are likely for weeks following a strong earthquake such as this one," it said.
The State Department said it was setting up an e-mail address and telephone number to handle inquiries from people with relatives in Japan.
(Additional reporting by Arshad Mohammed, David Alexander and Paul Eckert; editing by Philip Barbara)