President-elect Joe Biden is expected to nominate Jake Sullivan as his national security adviser and Linda Thomas-Greenfield as U.S. ambassador to the United Nations, multiple sources familiar with the plans told NBC News.

Sullivan served in the Obama administration as national security adviser to then-Vice President Biden before serving as director of policy planning at the State Department and as deputy chief of staff to then-Secretary of State Hillary Clinton. Sullivan later served as a senior policy adviser to Clinton's 2016 presidential campaign.

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Thomas-Greenfield served as the assistant secretary of state for Africa from 2013 to 2017 under former President Barack Obama. Before that stint, she served as U.S. ambassador to Liberia.

The news comes one day before incoming White House chief of staff Ron Klain said Biden will begin publicly naming his Cabinet officials. NBC News reported Sunday that former deputy secretary of state Antony Blinken is expected to be named secretary of state.

It is expected the role of U.N. Ambassador will be elevated to a Cabinet-level position in a Biden administration, two sources told NBC News.

At the outset of the Trump administration, Nikki Haley, then-U.S. ambassador to the United Nations, enjoyed Cabinet-level status but after she left in 2018, the position was no longer part of the Cabinet. Under Obama, the position was Cabinet level. Whether or not the position is Cabinet level is under the president's discretion. Read more at NBC News