US President Donald Trump shakes hands with US Army Lieutenant General H.R. McMaster (L) as his national security adviser at his Mar-a-Lago resort in Palm Beach, Florida.

United States President Donald Trump has named US Army Lieutenant General H.R. McMaster as his new national security adviser on Monday, taking over the post left vacant after Michael Flynn’s resignation.

Trump called McMaster, a career Army officer and prominent expert on counterinsurgency warfare, a “man of tremendous talent and tremendous experience.”

“He is highly respected by everyone in the military and we’re very honored to have him,” Trump told reporters at his Mar-a-Lago residence in Palm Beach, Florida.

He spoke sitting alongside McMaster, who was dressed in uniform. Trump said McMaster would work alongside acting national security adviser Keith Kellogg, a retired three-star general, in a “very, very special” collaboration.

McMaster, who heads the Army Capabilities and Integration Center and is deputy commanding general of the Futures Center at US Army Training and Doctrine Command at Fort Eustis, previously directed a transparency task force in Afghanistan.

He also held key roles in the Iraq War and Gulf War, and is known for his criticism of the US military’s involvement in the Vietnam War.