"I want to assure the American public and our allies and partners that the Department of Defense remains strong and continues its vital work of protecting our homeland, our people and our interests around the world," Acting Secretary of Defense Christopher Miller said.

Miller was named to the position on November 9 after Trump fired Mark Esper, his fourth defense secretary in four years.

With no experience managing a massive workforce like the Pentagon, Miller, a former special forces officer and a White House counter-terrorism specialist, will likely be replaced soon after President-elect Joe Biden takes office on January 20.

But his arrival at the Pentagon, together with several other Trump loyalists with little or no Department of Defense experience, raised concerns that the US military establishment could pass several weeks under weak leadership.

Miller though has reached out by telephone to fellow defense chiefs in France, Britain, and Germany, and plans to speak later Friday with NATO head Jens Stoltenberg, to reassure Washington's most important allies.

He has also spoken to Mitch McConnell, the Republican Senate majority leader, and Speaker of the House Nancy Pelosi, the top Democrat.

Miller made the comment as he welcomed visiting Lithuanian Minister of Defense Raimundas Karoblis.

"This is my first official function and I cannot imagine a more important visitor," he said.

He then remarked on a plaque in Vilnius which carries words spoken by president George W. Bush in 2002, when Lithuania joined NATO: "Anyone who would choose Lithuania as an enemy has also made an enemy of the United States of America."