US President Donald Trump on Monday named Army Lt. Gen. H.R. McMaster as his new national security adviser, succeeding Michael Flynn, who left last week amid criticism of his pre-inauguration contacts with the Russian ambassador.

"General H.R. McMaster will become the national security adviser. He's a man of tremendous talent and tremendous experience," Trump, who was accompanied by the general, said in a surprise announcement at his Mar-a-Lago estate in Palm Beach, Florida.

"I watched and read a lot over the last two days. He is highly respected by everyone in the military and we're very honored to have him," the president added.

McMaster, who holds a PhD in military history and is the author of a book - "Dereliction of Duty" - that criticizes the "lies" that led to the United States' involvement in the Vietnam War, had not been regarded as one of the frontrunners for the post, reported EFE.

Much like Trump’s pick to head the Pentagon, James Mattis, McMaster is a known entity to traditional US allies, and a figure reassuring to the US security establishment Trump has often scorned, reported The Guardian.

During the announcement at Trump’s Mar-a-Lago club in Florida, McMaster thanked Trump for the appointment and looked “forward to joining the national security team and doing everything that I can to advance and protect the interests of the American people”.

Yet it remains to be seen whether McMaster’s imminent arrival at the White House will settle an ongoing struggle for the future course of national security and foreign policy. At least one other candidate for the job, McMaster’s ally David Petraeus, dropped out of the running after insisting on the independence to select his own staff.

The nomination of McMaster comes after the controversial resignation of Michael Flynn, opening one of the biggest crises of Trump's first month in office.