The chairman of the US Joint Chiefs of Staff, Admiral Michael Mullen, has confirmed reports that Pakistan is increasing its nuclear weapons programme, but has provided no details. The confirmation came during a Senate Armed Services committee hearing on Thursday when Democrat senator Jim Webb, an expert on defence issues, raised fears that Pakistan is adding to the nuclear weapons it traditionally has pointed toward India, and questioned whether US aid could be funding it. Noting reports that Pakistan "may be actually adding on their weapon systems and warheads" Webb asked: "Do you have any evidence of that?" "Yes," Mullen answered. Webb said that is a cause for "enormous concern," because with the militant threat, he said, Pakistan's government is not very stable. The US has urged Pakistan to focus on the extremist threat instead of India. But Mullen told senators that it's still unclear that Pakistani leaders can shift their focus for a long period even as they slowly acknowledge that militants pose more of a security risk. "Historically, they haven't done that," Mullen said. "So right now, I'm encouraged by what's happened, but I certainly withhold any judgment about where it goes because of the historic lack of sustainment, and they know they need to do that." Also at the hearing, Admiral Mullen said it is not only Pakistan's top leaders who need to recognise the militant threat. He said Pakistan's powerful intelligence service, the ISI, must also change its approach, and one key to that is convincing its leaders there will be a long-term US commitment to helping them defeat the militants. "The ISI in the long run has to change its strategic thrust and get away from working both sides," he said. "That's how they have been raised, certainly over the last couple of decades, and that's what they [are going to continue to] believe, until they think we're going to be there for a while." Asked by Senator John McCain, Republican presidential opponent of Barack Obama, whether he still worried "about the ISI cooperating with Taliban?", Mullen simply said: "Yes, sir." Several senators voiced doubts about sending millions of dollars to Pakistan without assurances it will be spent to fight extremists who threaten security and political stability both there and in Afghanistan. Next year's Pentagon budget includes $700 million to train and otherwise help Pakistan fight insurgents.