US Defense Secretary Chuck Hagel will resign after less than two years in the top military post, media report.

President Barack Obama is expected to confirm Chuck Hagel’s resignation in a White House address later on Monday morning.

Chuck Hagel, 68, a Vietnam war veteran and former senator, became defence secretary in 2013.

Last month, it was reported that Chuck Hagel was sharply critical of the US strategy against Islamic State (ISIS) and in relation to the Syria regime.

He is expected to stay on as secretary until his successor is confirmed.

An unnamed official told the Associated Press that Chuck Hagel and Barack Obama both “determined that it was time for new leadership in the Pentagon” and had been discussing the move for weeks.

The New York Times reported that Barack Obama had asked Chuck Hagel to step down after the defense secretary opened up discussions of his leaving.

Chuck Hagel, who served as Republican senator for his home state of Nebraska for 12 years, became critical of US involvement in Iraq despite voting to authorize the war.

He replaced Leon Panetta as defense secretary in Barack Obama’s second term, taking on the task of winding down the Afghanistan war and making a military shift towards Asia.

The future of US military policy has changed amid air strikes against ISIS in Iraq and Syria.

US media report there was increasing tension between Chuck Hagel and the administration over decisions in Syria and working styles, citing Hagel confidantes and senior defense officials.

Barack Obama is not expected to announce a nominee to replace Chuck Hagel on November 24. One named, the nominee would have to be confirmed by the Senate.

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