LONDON (AFP/Reuters) - Britain and the US on Friday defended their strategy in Afghanistan amid mounting criticism over the rising death toll from war-weary voters. The incident of Nato airstrike came as British Prime Minister Gordon Brown delivered a speech calling the Western strategy against insurgents in Afghanistan flawed yet essential to suppressing the worldwide terrorism threat. Top US military chiefs launched a staunch defence of their campaign against the Taliban before a war-weary public and warned that time was running out to make headway. But a keynote speech by British Prime Minister Gordon Brown was overshadowed by the resignation of a ministerial aide in protest at Londons stance in Afghanistan, where 212 British soldiers have been killed in the campaign. In Washington, US Defence Secretary Robert Gates insisted on Thursday that the war was not slipping through the administrations fingers, but admitted: There is a limited time for us to show that this is working. We are mindful of that, we understand the concerns of many Americans in that area but we think that we now have the resources and the right approach to start making some headway, Gates told reporters. British Premier Brown pledged that Britain will not walk away from Afghanistan when its own security was at stake. People ask what success in Afghanistan would look like. The answer is that we will have succeeded when our troops are coming home because the Afghans are doing the job themselves, he told the International Institute of Strategic Studies (IISS). His message was clouded by the resignation late Thursday of Eric Joyce, a parliamentary aide to Defence Secretary Bob Ainsworth, who warned there were problems in Afghanistan which need fixing with the greatest urgency. Joyce, a lawmaker and former army major, also criticised Nato allies in Afghanistan, saying many of them do far too little, leaving Britain to shoulder more of the combat role. When the security of our country is at stake we cannot walk away, Brown said. Finance Minister Alistair Darling said it was vital to support the governments in Afghanistan and Pakistan. US Joint Chiefs of Staff Chairman Admiral Michael Mullen stressed that there is a sense of urgency and time is not on our side in Afghanistan - but he rejected some commentators suggestions that US troops withdraw now. Theres no way to defeat Al-Qaeda, which is the mission, with just that approach, you cant do it remotely, you cant do it offshore, Mullen said. I certainly dont think its time to leave. Gates and Mullen declined to detail the findings of McChrystals report, which has been forwarded to President Barack Obama and is being evaluated by senior military officials.