|Obama, left, announced the nominations of his new national security team on Thursday [AFP]
Barack Obama has announced a major reshuffle of the US national security team aimed at ensuring leadership continuity.
The US president on Thursday nominated Leon Panetta to replace Robert Gates as the defence secretary following his planned retirement this year.
General David Petraeus and Ambassador Ryan Crocker were named as Central Intelligence Agency (CIA) chief and US ambassador to Afghanistan, respectively.
The Senate has to approve the changes, which come as the US administration confronts numerous national security challenges at home and abroad.
"These are the leaders that I've chosen to help guide us through the difficult days ahead," Obama said in the White House with Gates, Panetta, Petraeus and other top officials by his side.
"I will look to them and my entire national security team for their counsel, continuity and unity of effort that this moment in history demands."
Panetta is the current CIA director while Petraeus currently heads military operations in Afghanistan.
The long-anticipated changes is expected to place a long-standing Democratic Party figure at the head of the Pentagon as Obama presses forward with politically delicate policies in Afghanistan and Libya.
The administration and congress also face mounting calls for defence spending cuts as the US looks for ways to narrow the US budget deficit, which stands at $1.4tn this year.
Gates was appointed by former president George Bush, a Republican, and has proved to be an outspoken on key issues under both administrations.
Gates, himself a former CIA director, had made it clear that he would step down as defence chief this year.
Panetta is a former US representative from California who served as chairman of the House Budget Committee. He was former president Bill Clinton's budget director, then chief of staff.
Petraeus is credited with pulling Iraq from the brink of civil war after the 2003 US invasion before he assumed command of US and NATO forces in Afghanistan.
Before word of the reshuffle broke, some Washington insiders suggested the White House wanted a prominent position for Petraeus to ensure he would not be tapped by Republicans to challenge Obama next year.