Caroline Kennedy, the daughter of the late President John F. Kennedy, is a leading candidate to become President Barack Obama's nominee as ambassador to Japan, two sources said.

Kennedy, 55, would replace John Roos, a former technology lawyer and Obama campaign donor, as U.S. ambassador, according to the sources who asked for anonymity because the decision hasn't been made official.

While the president has signed off on Kennedy's nomination, her vetting for the post hasn't been completed, one of the sources said.