Defense Secretary Robert Gates said both the U.S. and Afghan governments agree the U.S. military should remain involved in the training of Afghan troops after the planned 2014 end of combat operations.
Gates, who arrived today in Afghanistan on an unannounced visit, made the remarks to a group of U.S. troops at Bagram air base, which is headquarters for U.S. and NATO forces in eastern Afghanistan.
Gates was due to meet with Afghan President Hamid Karzai.
During his two-day visit, Gates plans to travel to eastern and southern portions of Afghanistan, the areas most fiercely contested by the Taliban insurgency.
His arrival comes amid fresh tensions after NATO helicopters mistakenly killed nine Afghan children on March 2 in eastern Afghanistan.
NATO's international force in Afghanistan said it mistook the children for rebels who had earlier attacked a nearby U.S. military base in Kunar Province.
Afghan President Hamid Karzai told the commander of U.S. and NATO forces in Afghanistan, General David Petraeus, that his apology over the incident was "not enough."
Karzai told Petraeus at a March 6 meeting in Kabul that civilian casualties in the almost decade-old war are "no longer acceptable."
Earlier in the Afghan capital, hundreds chanting "Death to America" protested over the killing of Afghan civilians by foreign forces.
There have been at least four incidents of civilian casualties in eastern Afghanistan in the past two weeks in which Afghan officials say more than 80 people have died.
After the latest incident, Radhika Coomaraswamy, the United Nations Special Representative for Children and Armed Conflict, called for a review of air strikes by foreign forces in Afghanistan.
compiled from agency reports