LONDON (AFP) - Peace will only come to Afghanistan if Pakistan can sort out the militants on its side of the border, where US strikes are not helping, the head of Britain's armed forces told The Sunday Times newspaper. Air Chief Marshal Sir Jock Stirrup said only politics, long term, could bring peace on both sides of the frontier. The chief of the defence staff said that weaknesses in Afghan President Hamid Karzai's government were causing difficulties for the 8,300 British troops battling Taliban insurgents in the troubled south of the country. "The weakness of governance in Afghanistan worries me considerably," Stirrup told the weekly broadsheet. "But governance is not just about what goes on in Kabul. We have to look at the wider picture. "The Taliban movement - and Taliban is now a catch-all phrase for ideologues, criminals, people with tribal grudges, people who are quite simply guns for hire to keep bread on the table - is on both sides of the border. "It makes no distinction between one side or the other. Some people move across. Some are based almost exclusively in Pakistan. Some are based exclusively in Afghanistan. "It's impossible to distinguish between those two and actually, in my view, not necessary. The border is not relevant." Stirrup sympathised with the difficulties faced by the Pakistani military, admitting that its success so far had been 'limited'. "The Pakistan army has a series of very considerable problems," he said, adding it had realised that 'the growing insurgency within its own borders is an existential problem for Pakistan'. General Ashfaq Kayani, the head of Pakistan's army, "is absolutely clear on the size of the challenge that he faces. "The Pakistan army has become much more sophisticated and much more flexible and adaptable in terms of its approach. "So we have to do all we can to support the military in that shift, but we have to recognise that they can't do it overnight. "Just as in Afghanistan, that kind of insurgency cannot be defeated by conventional military means. It can only be dealt with, in the long term, through politics." He said it was 'very important' for the Islamabad government to start changing public sentiment that all would be well if western troops were not in Afghanistan. "While they shouldn't be driven by public opinion, they can't operate in the face of it. The Predator strikes don't help in that regard," he said, referring to US airstrikes on the Pakistani side of the border.