“[First Lady] Michelle and I send our deepest condolences to the people of Japan, particularly those who have lost loved ones in the earthquake and tsunamis,” he said in a statement.
“The United States stands ready to help the Japanese people in this time of great trial. The friendship and alliance between our two nations is unshakable.”
Vice President Joe Biden also offered the “thoughts and prayers of the American people” during an official visit to Moldova.
“We, the United States, stand ready to do anything we can to help our Japanese friends as they deal with the aftermath of this tragedy,” Biden said.
Obama said he would monitor the tsunami triggered by the earthquake, which struck his home state of Hawaii and expected reach the US West Coast in the coming hours, and had instructed emergency responders to be prepared.
Also on Capitol Hill, senate foreign relations committee chairperson John Kerry said the United States “stands shoulder-to-shoulder with the Japanese people during this time of need”.
“We will spare no effort now as rescue and recovery operations get underway in Japan,” he said.
State department spokesperson Philip Crowley said US officials “have been in touch with the Japanese government and we stand ready to provide whatever assistance needed in response to the tsunami”.
He also said US Ambassador John Roos had moved the Tokyo embassy’s command centre to an alternate location due to “the many aftershocks in Tokyo”.
The 8.9-magnitude quake, the strongest ever recorded in Japan, unleashed a terrifying tsunami that claimed hundreds of lives.