The U.S. defense secretary says there is no single way to destroy al-Qaida, but the killing of its leader Osama bin Laden has crippled the group.

Leon Panetta said late Friday “the more successful we are at taking down those who represent their spiritual, ideological leadership, the greater our ability to weaken their threat to this country.”

Panetta said he was certain the U.S. was safer since the death of bin Laden, who was killed on May 2 last year in a secret Navy SEAL operation in a walled-off compound in the Pakistani garrison town of Abbottabad.

Robert Cardillo of the Office of the Director of National Intelligence made a similar comment Friday, saying the likelihood of an attack using chemical, biological, atomic or radiological weapons over the next year is low.

However, other U.S. intelligence officials, speaking on condition of anonymity said Friday, while al-Qaida's core network is probably not capable of carrying out another mass-casualty attack on the scale of September 11, 2001, the terrorist group's affiliates remain a threat.

The officials singled out al-Qaida's Yemeni offshoot as especially dangerous, saying it is gaining territory and followers, despite targeting by Yemeni and U.S. counter-terrorist forces.

The anonymous officials also cited the threat of terrorism from so-called “lone wolves” who are inspired by al-Qaida and are intent on committing violence. They said attacks like the shooting spree last month in France by an Islamic militant are difficult to counter.

The Washington Post reported Friday Pakistan's intelligence service believes it deserves credit for helping the U.S. locate bin Laden's hideout. The newspaper reported the unnamed officials say Pakistan intelligence gave the U.S. information, resulting in the U.S. finding bin Laden's residence. Washington has disputed their claims.

Meanwhile, U.S. President Barack Obama has taken the extraordinary step of giving a television interview in the White House Situation Room about how he made the decision to send the special forces to Pakistan to kill bin Laden. The Situation Room is where the president and other top U.S. officials watched live video of the raid as it took place. The interview is scheduled to air on NBC May 2, the anniversary of the raid. NBC News President Steve Capus said the interview will be the “definitive account” of the operation.

The New York Times said Friday Mr. Obama's concerted effort to “trumpet” the killing of bin Laden as “the central accomplishment” of his presidency places the U.S. leader, who is up for re-election this year, on the “unusual route of bragging about how he killed a man.” President Obama's campaign has released a video showing former president Bill Clinton praising Mr. Obama for making the call to carry out the risky raid. Mr Clinton also questions whether Mitt Romney would have made the same decision.