U.S. President Barack Obama on Thursday conveyed his "deepest and heartfelt" condolences to the families of the victims in the sinking of a passenger ferry of the Republic of Korea (ROK) and vowed to render all assistance requested by the latter.

"Our hearts ache to see our Korean friends going through such a terrible loss, especially the loss of so many young students," Obama said in a statement issued by the White House. "I've directed our military to provide any and all assistance requested by our Korean partners in the days ahead."

The passenger ship with 475 people aboard, mostly high school students, capsized in waters off the southwest coast of ROK early Wednesday morning. Twenty people were so far confirmed dead and more than 270 others remained missing, according to reports.

American Navy personnel and U.S. Marines are already on the scene assisting with the search and rescue efforts, said Obama, reiterating the "unwavering" U.S. commitment to the ROK, which is part of his four-nation Asian trip next week, while promising ROK will have the "unending support" of the United States.