The approval of retired Marine General James Mattis to be secretary of defense and Marine General John Kelly to be Secretary of Homeland Security came on January 20 after Trump was sworn in as president, RFE/RL reported.

Mattis has not always totally agreed with comments made by Trump, specifically about the NATO alliance.

Read alsoReuters: Trump, sworn in as U.S. president, promises to put 'America First'On January 12, he called NATO "the most successful military alliance probably in modern history, maybe ever" and said Russia poses a threat to it.

Mattis's nomination as defense secretary had attracted concern among some members in Congress, due to a U.S. law barring military officers from becoming the civilian head of the Defense Department within seven years of retiring from the military.

However, he was granted a waiver in the House and Senate that would allow him to serve.