Terrorist threat to US has 'metastasized' since 9/11 attacks

The increasingly diffuse scope and nature of terrorist threats facing the United States since the Sept. 11 attacks will force Washington to depend on its international allies more than ever before. 

"The challenge of terrorism has evolved as it has metastasized since 9/11," Defense Secretary Chuck HagelCharles (Chuck) Timothy HagelShould Mike Pompeo be confirmed? Intel chief: Federal debt poses 'dire threat' to national security Hagel: Trump is 'an embarrassment' MORE said on Tuesday. 

While al Qaeda's core leadership has been bloodied by U.S. counterterrorism operations in the years after 9/11, its operational cells in Africa, the Mideast and elsewhere have grown in strength and lethality. 

Intelligence on a looming terror atttack by the group's Yemeni-based cell, known as al Qaeda in the Arabian Peninsula (AQAP), forced the State Department to shutter several U.S. embassies and consulates in the Mideast earlier this year. 

French forces, backed by U.S. airpower and intelligence, launched a massive counterterrorism offensive against al Qaeda's West African faction, dubbed al Qaeda in the Islamic Magreb (AQIM), after the group took over large portions of northern Mali. 

While these cells remain scattered across the globe, "many share a common [goal] regardless of state-to-state differences or political ideologies," Hagel said during a keynote speech at the Center for Strategic and International Studies. 

"This has required and will continue to demand unprecedented collaboration with partners and allies on counterterrorism efforts," according to the Pentagon chief. 

This unprecedented dependence on international allies in U.S. counterterrorism operations is being accelerated by massive, across-the-board budget cuts facing the Pentagon and intelligence community under sequestration. 

The pending loss of personnel, materiel and capabilities due to sequestration will force the United States to look to foreign militaries and intelligence agencies to pick up the slack. 

While Hagel did predict a whole new level of interdependence between Washington and its allies on counterterrorism operations, he did not indicate the United States was ready to abandon unilateral efforts to decimate al Qaeda and other radical militant groups. 

But those efforts, including the controversial use of armed drone strikes and clandestine "kill/capture" missions could undermine U.S. efforts to build bridges with foreign forces in hot spots around the world. 

Most recently, Pakistan threatened to shutter key U.S. supply lines into and out of Afghanistan in response to an American drone strike that killed the reputed chief of the Pakistani Taliban. 

Hakimullah Mehsud and five other Taliban members were reportedly leaving a mosque outside the Dande Darpakhel area of North Waziristan when their vehicle was hit, intelligence officials in Peshawar said last Friday.  

Mehsud had been a top high-value target of U.S. military and intelligence counterterrorism operations for the past decade. 

But his killing by American forces inside Pakistan's borders, an issue that has continually riled U.S.-Pakistani relations, has enraged the country's leaders and reignited the debate over the critical Afghan supply lines. 

Libyan officials also voiced outrage over the capture of top al Qaeda leader Abu Anas al-Libi by U.S. forces. 

Members of 1st Special Forces Operational Detachment-Delta, known as Delta Force, took custody of al-Libi -- a Libyan national -- during a daylight capture mission in Tripoli in early October. 

Tripoli characterized the U.S. operation as a "kidnapping" of a Libyan citizen, demanding an explanation from the White House for the mission. 

Al-Libi was remanded to the custody of the Justice Department after being interrogated by U.S. military and intelligence officials aboard the U.S.S. San Antonio somewhere in the Mediterranean for a week and a half.