US forces have decimated al Qaeda's leadership and made gains against some of its affiliates, but the fight has shifted in new directions that will require persistent US efforts to truly end the threat, Defence Secretary Leon Panetta said.

Panetta, in a speech to the Centre for a New American Security, said while the United States had achieved progress against al Qaeda affiliates in Yemen and Somalia, associated groups had made inroads in Mali and Nigeria and were trying to gain a foothold in Libya.

He said the United States had "decimated core al Qaeda," killing leaders like Osama bin Laden, Sheikh Saeed al-Masri and Abu Yahya al-Libi. It also has made strides against affiliated groups like al Qaeda in the Arabian Peninsula in Yemen and al Shabaab in Somalia, he said.

"These gains are real, but it is important to point out that even with these gains, the threat from al Qaeda has not been eliminated," he said. "We have slowed the primary cancer, but we know that the cancer has metastasized to other parts of the global body."

As a result of US pressure, Panetta said, al Qaeda has become even more "widely distributed, loosely knit and geographically dispersed."

"The fight against al Qaeda has taken a new direction - one that demands that we be especially adaptable and resilient as we continue the fight," he said.

Panetta said disrupting and ultimately defeating al Qaeda would remain a key priority even as US forces draw down in Afghanistan over the next two years and renew their focus on the Asia-Pacific region as part of a new military strategy.

He said the key to achieving "the end of al Qaeda" was to finish the job in Afghanistan in a way that ensured the group could never again establish safe havens there.

Panetta said dealing with government corruption in Afghanistan and eliminating militant safe havens in Pakistan were crucial to Afghan stability.

"It will require continued commitment by the international community and the United States to help Afghan forces achieve it," he said, adding, "We have come too far and invested too much blood and treasure" not to finish the job.

He said the United States also would have to keep the pressure on al Qaeda in Pakistan, Yemen and Somalia. It would also have to work to prevent the emergence of al Qaeda safe havens elsewhere in the world, using US special operations forces in partnership with local forces, he said.

"To truly end the threat from al Qaeda, military force aimed at killing our enemy alone will never be enough," Panetta added. "The United States must stay involved and invested through diplomacy, development, education and trade in those regions of the world where violent extremism has flourished."

He said that included Afghanistan and Pakistan as well as countries in the Middle East and Africa.

- Reuters