Prensa Latina News Agency quoted Obama to have said in a speech at the White House that this had not been an easy decision, but at the same time, he said this was the time for Hagel to leave his post.

According to the newspaper The New York Times, the president had requested the resignation of the head of the Pentagon, due to differences on the strategy to adopt in the offensive against the radical Islamic State, said to be the main danger to this country's national security.

Hagel's resignation is the first change by Obama in his cabinet, after the defeat to the democrats at the mid-term elections on November 4, in which republicans won the majority of both congressional chambers.

Republican former senator, who had been the secretary if defense until now, assumed the post in early 2013. Hagel will remain in his post until the Senate confirms his successor.