WASHINGTON (AP) _ President Barack Obama said he was ``heartbroken'' by images of devastation in Japan following Friday's deadly earthquake and tsunami, and pledged U.S. assistance to help the country recover.

   ``Our hearts go out to our friends in Japan and across the region, and we're going to stand with them as they recover and rebuild from this tragedy,'' Obama said during a White House news conference.

   Hundreds were dead or missing in Japan following Friday's 8.9 magnitude earthquake _ the largest in Japan's history _ and the accompanying tsunami. The West Coast and several islands in the Pacific were also under tsunami warnings, through no major damage was reported in the U.S. as the first waves swamped Hawaii's beaches and grazed the coastline of the mainland.

   Obama said he was confident that Japan would successfully rebound from the potentially ``catastrophic'' disaster, and offered his condolences to the families of those who were killed.

   ``When you see what's happening in Japan, you are reminded that for all our differences in culture or language or religion, that ultimately humanity is one,'' Obama said.

   Obama spoke with Japanese Prime Minister Naoto Kan earlier Friday, and said the Japanese leader told him there were no radiation leaks from Japan's nuclear power plants. The Japanese government ordered thousands of residents near a plant in the city of Onahama to move back at least two miles from the plant. The reactor was not leaking radiation but its core remained hot even after a shutdown.

   One U.S. aircraft carrier is already in Japan, and a second is on its way to assist with the recovery efforts. A U.S. ship was also heading to the Marianas Islands.

   Obama's chief of staff Bill Daley notified the president about the earthquake in Japan at 4 a.m. Washington time. Obama activated the Federal Emergency Management Agency, and huddled with senior advisers at the White House to discuss plans to assist Japan, as well as the U.S. states and territories that could be affected.

   Pentagon spokesman Col. David Lapan said U.S. and Japanese officials are talking constantly to determine what type of assistance is needed. He said aid could include food, water, shelter, and medical supplies.

   The State Department said no Americans were killed or injured in Japan; there were also no reports of damage to U.S. installations or ships in the area. The department issued a travel alert, strongly urging U.S. citizens to avoid non-essential travel to Japan.