Washington: US Defense Secretary Chuck Hagel has resigned, the first major change to President Barack Obama's cabinet since his Democrats were routed in midterm elections three weeks ago.
Hagel was appointed less than two years ago as Obama pushed his signature program of winding up wars in Afghanistan and Iraq, a process that is being upended this year with US re-engagement in Iraq and greater military cooperation with Kabul.
"The Secretary was brought in to manage a period of transition for the Pentagon," a U.S. defense official said, suggesting that period had closed.
Obama was to announce Hagel's resignation at a White House.
Hagel, who had struggled to improve his ties with Congress after a contentious 2013 confirmation hearing, submitted his resignation letter after lengthy discussions with Obama that began in October, officials said.
"A successor will be named in short order, but Secretary Hagel will remain as Defense Secretary until his replacement is confirmed by the United States Senate," a senior Obama administration official said.
Hagel had raised questions about Obama's strategy toward Syria in a two-page internal policy memo he wrote that leaked. In it, he warned that Obama's policy was in jeopardy due to its failure to clarify its intentions toward Syrian President Bashar al-Assad.
Obama has insisted that the United States can go after Islamic State militants without addressing Assad, who the United States would like to leave power.