U.S. President Barack Obama said on Monday it would be very difficult for al Qaeda to launch another major attack on the United States, as its leadership has been decimated.

U.S. special forces killed al Qaeda leader Osama bin Laden in May at his hideout near Islamabad and U.S. strikes with aerial drones have killed senior militants in Pakistan's border areas with Afghanistan and in Yemen.

Asked by ABC News whether the strategic defeat of al Qaeda was at hand, Obama said: We have done more in the last couple of years than any time in the last 10 years to bring that about.

Obviously the most prominent case was us getting bin Laden but, when you look at the entire leadership tier of al Qaeda, they have been decimated, he said in the live interview.

The militants, who shocked the United States in 2001 with the Sept. 11 attacks using hijacked passenger planes, are rapidly approaching the point where they just cannot replace skilled operatives through their training, Obama said.

The United States, because of its open society, is always going to be vulnerable and al Qaeda is still dangerous and still our number one enemy, he said.

But I think we're in a position over the next couple of years, if we stay on it, that it's going to be very difficult for them to mount the kind of spectacular attacks that we saw on 9/11, Obama said.