US president George Bush has assured Afghan president Hamid Karzai that Washington will stand by Afghanistan, despite the approaching transition of power in the White House. He made the comments on a previously unannounced visit to Kabul this morning. After flying in to Bagram air base under cover of darkness, Bush first addressed US troops.. before going on to hold talks with Karzai in the presidential palace in Kabul. Bush had travelled to Kabul from Baghdad.. where a farewell visit to the Iraqi capital was marred by a shoe-throwing incident.