Washington: President Barack Obama has said that the entire al-Qaeda leadership has been decimated and it would be "very difficult" for the group to stage a spectacular terror attack on the scale of the 9/11 strikes in near future.

"When you look at that entire leadership tier of al-Qaeda, they have been decimated. And they are rapidly approaching the point where they just cannot replace trained, skilled operatives who could threaten," Obama said.

"I think that we have done more in the last couple of years than anytime in the last 10 years to bring that about.

Obviously the most prominent case was us getting bin Laden," he said in response to a question. Obama conceded that the US is still not free from any possible terrorist attack.

"I think that given the nature of our open society, we're always going to be vulnerable to the possible terrorist attack," he said.

"But for them to be able to mount something that is a big project with a lot of financing, that is very difficult for them to do now. They're still dangerous. They're still our number-one enemy. We've got to make sure that we don't let up," he argued.

"We are in a position where over the next couple of years if we stay on it, that it's going to be very difficult for them to mount the kinds of spectacular attacks that we saw on 9/11," Obama added.