Australian Prime Minister Julia Gillard has vowed to support the US-led mission in Afghanistan during a surprise visit to troops in the war-torn nation on her first overseas trip as leader.Gillard, who arrived at the Australian-US base at Tarin Kowt yesterday, spent two hours with the troops, assuring them there would be no dilution of the war effort, and thanking them for their guts and determination and bravery.Gillard, who is en route to a summit in Brussels, then left the base for the Afghan capital Kabul, where she met the overall allied commander in Afghanistan Gen David Petraeus.Gillard also met Afghan President HamidKarzai and then she spent about 12 hours in total in the country.Gillard is the third Australian prime minister to visit Afghanistan since the war began nine years ago and her trip came against the backdrop of growing unrest at home about the war.The federal Opposition has proposed boosting both personnel and equipment – including tanks, helicopters and artillery – in response to complaints from troops on the ground that they are being stretched too thin as their area of operations expands.Australia troop numbers in Afghanistan are currently 1550.