Trump nominates army veteran Mark Esper as new defence secretary

US President Donald Trump has nominated Mark Esper, an Army veteran, to be the next defence secretary, as the Pentagon faces a leadership vacuum amid a mounting confrontation with Iran.

The decision comes as lawmakers increasingly pressure the president to bring stable civilian leadership to the Pentagon after Jim Mattis abruptly resigned as defence secretary late last year.

The nomination of Esper, who is currently serving as the Secretary of the Army and previously served as a Vice President for Government Relations at the Raytheon Company, comes days after Patrick Shanahan withdrew his nomination from the top Pentagon position.

The US Senate needs to confirm his nomination before Esper can be sworn in as the Defence Secretary.

His first and most pressing task will be overseeing an expanding presence in the Middle East as tensions with Iran rise and it appears the President and key members of his national security team are at odds over how to respond to Tehran.

Tensions with Iran have increased since the Trump administration withdrew from the 2015 Iran nuclear deal last year.

On Thursday night, Trump ordered then canceled strikes on Iran after the Middle Eastern country downed an unmanned US drone. On Friday, the president said he decided not to carry out the strikes after deciding the potential deaths from the attack would not be "proportionate" to losing the drone.

Esper began his career as an Infantry Officer in the 101st Airborne Division, serving with distinction in the first Gulf War. He later served on active duty in Europe and on the Army Staff in Washington, DC, before transitioning to the National Guard and retiring after 21 years of service, the White House said.

He was an airborne ranger and recipient of the Legion of Merit, Bronze Star, and Meritorious Service Medals, among other awards and qualifications.

Esper worked on national security issues on Capitol Hill for Senators Chuck Hagel, Fred Thompson, and Majority Leader Bill Frist.

He was also a professional staff member on the Senate Foreign Relations and House Armed Services Committees, and later a Deputy Assistant Secretary of Defence.

He is a graduate of the United States Military Academy, Harvard University John F Kennedy School of Government and George Washington University.

Trump also nominated David L Norquist to be Deputy Secretary of Defence and Ryan D McCarthy to be Secretary of the Army.