Top US officials renewed their defense of President Barack Obama's strategy in Afghanistan on Thursday as skeptical lawmakers questioned the costly mission and a July 2011 date to start an American withdrawal.

The president's plan to surge 30,000 troops to battle Afghan insurgents met with criticism from the both the right and the left, with Republicans opposed to a timeline for a pull-out and Obama's fellow Democrats anxious about sending yet more forces to fight for a corruption-plagued government in Kabul.