US President Barack Obama inspects a guard of honour with Afghan President Hamid Karzai at the presidential palace in Kabul on Sunday. Mr Obama arrived unannounced in Afghanistan on Sunday, his first visit to the war zone that could define his presidency. Air Force One landed in darkness at the Bagram airbase north of Kabul, from where he was whisked by helicopter to the presidential palace. He is expected to spend several hours in Kabul before the long flight back to Washington.  PHOTO: Reuters