US secretary of defence to step down

US Defence Secretary Chuck Hagel is to step down on Monday, a senior official told reporters, after criticism of the campaigns in Afghanistan and against the Islamic State group.

There are conflicting reports on whether he is resigning or has been forced from his post.

The 68-year-old former senator and Vietnam war veteran was to join President Barack Obama at the White House later in the day to jointly announce his departure.

"In October, Secretary Hagel began speaking with the president about departing the administration... Those conversations have been ongoing for several weeks," an administration official said. 

Over the past two years, Secretary Hagel helped manage an intense period of transition for the US Armed Forces. - White House official

"A successor will be named in short order, but Secretary Hagel will remain as defence secretary until his replacement is confirmed by the United States Senate."

Hagel, as a Republican senator, voted in favour of the 2003 US invasion of Iraq, but later became a critic of the drawn-out conflict that ensued. He was taken on by the Obama administration early last year to oversee the withdrawal of US forces from Afghanistan. 

Hagel's experience as a non-commissioned officer who saw action in Vietnam was seen as a strength as he took on the job, but his public appearances have often appeared clumsy or underwhelming as the US administration struggles to adapt to new conflicts. 

Hagel struck up a relationship with Obama when they were both on the Senate Foreign Relations Committee and were critical of the US campaign in Iraq. However, once in the Pentagon he is reputed to have struggled to integrate into the president's inner circle. He was the lone republican in the White House national security setup.

"Over the past two years, Secretary Hagel helped manage an intense period of transition for the United States Armed Forces, including the drawdown in Afghanistan, the need to prepare our forces for future missions, and tough fiscal choices to keep our military strong and ready," the official said.  

However, in recent months Hagel has largely been overshadowed by the chairman of the Joint Chiefs of Staff, General Martin E Dempsey.

Hagel came into office tasked with winding down the Afghanistan theatre of conflict and making a "pivot" towards Asia and the Pacific.

The development of the conflict in the Middle East and the US' expanding role within it has put increasing strain on the relations between Hagel and the administration.

The US strategy in the Middle East, and particularly towards the Islamic State group (IS, formerly known as ISIS), has come under attack from hawks and doves alike in Washington. Hawks are pushing for greater involvement from the air and on the ground. Doves are concerned with changing war objectives and the corresponding ramping up of military resources being assigned to the conflict.

The White House did not give any clue who might be Hagel's eventual replacement at the Pentagon, but the New York Times - which broke the news of his departure - cited three candidates.

Former under-secretary of defence Michele Flournoy is said to be in the running, along with Senator Jack Reed of Rhode Island - a former army officer - and former deputy secretary of defence Ashton Carter.