The United States' new defense secretary, Leon Panetta, has officially taken up his new post.

The former head of the Central Intelligence Agency was sworn in Friday at the Pentagon.

In a message to the defense department, he laid out his vision for confronting the challenges facing the military both at home and abroad.

He vowed to persist in the nation's efforts to defeat al-Qaida, calling the operation that killed Osama bin Laden a “major step toward that goal.”

On Afghanistan, Panetta said the U.S. must remain committed to working closely with its Afghan and international partners to ensure the country never again becomes a safe haven for al-Qaida and its allies. He said the U.S. must also cement a strategic relationship with the Iraqi government and help Iraq realize its potential to become a stable democracy in what he described as a “vitally important region in the world.”

Panetta also touched on defense budget matters, saying tough choices will need to be made to cut spending, but reiterating his belief that the Pentagon can achieve both fiscal discipline and a strong national defense.

Panetta is taking over the Pentagon at a time when President Barack Obama has called for an additional $400 billion in cuts to security spending.

He brings extensive budget experience to the Defense Department, having served as head of the White House budget office under President Bill Clinton, and before that, chairman of the House of Representatives Budget Committee.

Panetta's predecessor, Robert Gates, retired Thursday after serving under two administrations.

Panetta told U.S. troops in his message Friday that like Gates, he too will be a “tireless advocate” for them and their families.