WASHINGTON - Defence Secretary Robert Gates said the United States' biggest concern in the Afghan war is the threat posed by militant sanctuaries near the Pakistan-Afghanistan border. The threat is from "safe havens on the Pakistani side of the border, not only for al-Qaeda, but also for the Taliban" and other groups "working together," Gates said on NBC's "Meet the Press" programme. "After all, 20 years ago I was on the other side of that border as deputy director of the CIA, fighting the Soviets," Gates said, referring to the Central Intelligence Agency. "And we had the safe haven in Pakistan, and let me tell you, it made a big difference," he added. Meanwhile, Chairman US Joint Chiefs Admiral Mike Mullen acknowledged that the top Pakistani leadership is very much alive to the importance of dealing with terrorist threat on their Afghan border as he stressed cooperative efforts to curb insurgency on both sides of the Pak-Afghan border. He noted the Pakistani forces on their side of the border and the US-led international and Afghan forces on the Afghan side have pressured militants in the restive region. At the same time, Mullen recognised complexity of the challenge in the tribal border areas, where, he said, the issue of militant hideout needs to continue to be addressed. "He (the Pakistani Army Chief) knows and his leadership knows very specifically they have got a serious threat here, Not only this threatens us but it is also threatening them. They have seen violence go up dramatically in their country," he told CNN's State of the Union programme Sunday. The top US military officer said Pakistan is trying to address violence within its borders. Pakistani tribal area along the Afghan border is "extraordinarily complex - it has got a rich history, that I've studied hard to try to understand and engaged with leaders from all the countries" in trying to understand. "That's one of the reasons, I have been to Pakistan. I have met with (Army Chief) Gen Ashfaq Parvez Kayani ten times since last February and will continue to do that. I have that personal professional relationship of engagement." He also recognised Pakistan's concerns on its border with India. "Clearly, they are also concerned about the situation on their other border with India, that is longstanding. And I am hopeful that leaders will continue to use the kind of judgment and rhetoric that tamps that down overtime." Earlier, he told FOX News that "there is a continuing concern with the existence of the safe haven in the FATA in Pakistan, and that has to be addressed, has been addressed, and needs to continue to be addressed." "We've brought pressure on both sides of the border, Pakistani military as well as coalition forces and Afghan forces...and we need to continue to bring that pressure on both sides and continue to coordinate those operations." Agencies add: Top military and defence officials on Sunday declined to confirm or deny a suspected US missile strike in South Waziristan but said Washington was determined to counter militants operating on the border with Afghanistan. Asked if two suspected missile strikes were proof that President Barack Obama was escalating US attacks on Al-Qaeda and Taliban militants in Pakistan, top military officer Admiral Mike Mullen said: "Well, I'm not going to talk a lot about our operations specifically." But, according to a private TV channel, he said, the Predator drone attacks inside Pakistan were part of policy of obama. Mullen said it is "extraordinarily hard" to find Osama bin Laden, against whom the Washington has launched a massive manhunt post 9/11. "He's, obviously, a very, very difficult individual to find, I mean, extraordinarily difficult," Adm Mullen said. "It's not as if we don't have a considerable amount of effort pursuing that, and I'm certain that will continue, but he hides pretty well," Mullen said. US Defence Secretary Robert Gates also declined to discuss possible US missile strikes when asked about covert action possibly fomenting turmoil in Pakistan. "Well, I'm not going get into any intelligence operations," Gates told NBC in an interview aired Sunday. US defence chief Gates said US officials held productive talks with their Pakistani counterparts last week in Washington and said the US government wanted to help "enable" Islamabad to fight Al-Qaeda and associated groups operating on the border with Afghanistan. "I will just say that I think that the key here is our being able to cooperate with and enable the Pakistanis to be able to deal with this problem on their own sovereign territory," Gates said. "I believe based on my talks with the Pakistanis here in Washington this past week, that they clearly now understand that what's going on up there in that border area is as big a risk to the stability of Pakistan as it is a problem for us in Afghanistan," he said.