Rubio was arguably the most hawkish option on Trump's shortlist for secretary of state, according to Reuters.
Over the last several years Rubio has softened some of his stances to align more closely with Trump's views. The president-elect accuses past US presidents of leading America into costly and futile wars and has pushed for a more restrained foreign policy.
While Trump could always change his mind at the last minute, he appeared to have settled on his pick as of Monday, according to the sources, who requested anonymity to discuss private conversations.
Representatives for Trump and Rubio did not immediately respond to requests for comment.
MP/PR