Marco Rubio took office as Secretary of State after being sworn in by Vice President JD Vance. Rubio is one of the first of Trump's nominees to officially take office.
"It's an extraordinary opportunity. I am honored and privileged, I understand the responsibility that has been given to me, and I want to thank President Trump for his trust. We will work every second of the day to help him deliver on the agenda that the American people have entrusted to him," he said.
Among other things, Rubio said that Trump will put America's interests above everything.
"He will keep his promises. The main promise when it comes to foreign policy is that the priority of the US State Department is the United States," Rubio added.
"Everything we do has to be justified by the answer to one of these three questions: Does it make us stronger? Does it make us safer? And does it make us more prosperous? If it doesn't answer one of these three things, we won't do it," Rubio concluded.
And as Rubio is expected to be introduced at the US State Department, CNN reports that many career officials serving in senior roles there have been asked to step down from their posts.
"Most received the request before Monday's inauguration. They have served in senior management and policy positions, as well as assistant secretaries of state, sources said, and are among the most senior diplomats in the State Department," CNN reports.
While it is common for an incoming administration to place its own officials in senior roles, current career officials are staying put while the nominees await Senate confirmation. But this has raised concerns, according to CNN.
"This is almost certainly the first step towards a major purge and taking over the career foreign service," a former senior diplomat said according to CNN.
CNN has reached out to the State Department for comment on the matter. According to them, among those asked to resign is John Bass, who served as Undersecretary for Political Affairs, the third-highest position at the State Department.
In his remarks on the Friday before his departure, former Secretary Antony Blinken praised Bass and said that "there is no better Foreign Service officer in this generation than John Bass."
Meanwhile, Marco Rubio is expected to address State Department employees at headquarters in Washington on Tuesday.