The Obama administration has declared Afghanistan a major non-NATO ally of the United States.
The action is meant partly to facilitate close defense cooperation after the U.S. combat troops withdraw from Afghanistan in 2014 and as a political statement of support for the South Asian country's long-term stability.
On an unannounced visit to Kabul, U.S. Secretary of State Hillary Rodham Clinton announced the alliance Saturday at the U.S. Embassy. She was to meet later with Afghan President Hamid Karzai in Kabul.
The pair will also discuss U.S.-Afghan civilian and defense ties, and stalled Afghan reconciliation efforts.
Clinton will then head to Japan for an international conference on Afghan civilian assistance. Donors are expected to pledge around $4 billion a year in long-term civilian support.