Gordon Brown arrived in Kabul on an unannounced visit this morning for talks with Afghan President Hamid Karzai in which he stressed the UKs commitment to defeat the Taleban. Mr Brown, whose troops have this year faced Britain's deadliest fighting in a generation, said the next few months would be critical in Afghanistan as the United States and its allies ramp up their forces to try to turn the tide against Taliban insurgents. "What we need to show is that there's a determination to take on the Taliban and to weaken them, but also a determination on the part of the Afghan government to play a bigger part in the future in what is to be done," Mr Brown told reporters at Kandahar air field, where he spent the night bedding down ibnn forces accommodation before meeting Mr Karzai. It was the first time a British premier had stayed overnight in either Afghanistan or Iraq, and came at the start of a surprise pre-Christmas visit to the troops. Mr Brown said: "I wanted to be here with the troops to thank them for what they are doing. "I wanted to see what it was like working with them." As the war has grown less popular at home,Mr Brown has been even more prominent than other Western leaders in voicing mounting criticism of the government of Mr Karzai, whoe re-election in August vote was marred by widespread fraud. The Afghan leader lashed back in an interview last week, saying comments from Brown were "very unfortunate and very artificial. It is extremely insulting".