The non-NATO ally declaration allows for streamlined defense cooperation, including expedited purchasing ability of American equipment and easier export control regulations. Afghanistan's military, heavily dependent on American and foreign assistance, already enjoys many of these benefits. The non-NATO ally status guarantees it will continue to do so.
Afghanistan is the 15th such country to receive the designation. Others include Australia, Egypt, Israel and Japan. Afghanistan's neighbor Pakistan was the last nation to gain the status, in 2004.
Clinton insisted that progress was coming incrementally but consistently to Afghanistan after decades of conflict. "The security situation is more stable," she said. Afghan forces "are improving their capacity."
At the news conference, Karzai thanked the U.S. for its continued support.
Clinton repeated the tenets of America's "fight, talk, build" strategy for Afghanistan: defeat extremists, and win over Taliban militants and others willing to renounce violence and help in the long reconstruction of Afghanistan.
Fighting still rages as Afghan and U.S.-led coalition forces battle insurgents, mostly in the eastern part of the country. Although casualties have fallen among foreign forces as the United States and other nations begin a gradual withdrawal, 215 coalition soldiers were killed in the first six months of the year, compared with 271 in the same period last year.
Reconciliation efforts haven't gained steam. Still, Clinton said she was pleased to be meeting the foreign ministers of Afghanistan and Pakistan together at the conference in Tokyo. That three-way relationship is seen as critical to stabilizing Afghanistan.
Clinton, who flew to Kabul after attending a 100-nation meeting on Syria in Paris, stressed the importance of the pledges for civilian aid. Afghanistan's cash-strapped government depends heavily on foreign assistance, and any significant drop-off in that help after 2014 could set back the country's development.
Asked about the corruption that has plagued the Afghan government, Clinton said the U.S. was working hard with Afghan authorities to eliminate fraud, mismanagement and abuse. She said the meeting in Tokyo would include accountability measures to ensure that money sent to Afghanistan benefits the Afghan people.
"This is an issue the government and the people of Afghanistan want action on, and we want to ensure they are successful," Clinton said.
Nations that once gave more generously to Afghanistan are now seeking guarantees that their taxpayer money will not be lost to corruption and mismanagement.
International donors say that many promises to crack down on corruption have not been carried out. Some highly placed Afghan officials have been investigated for corruption but seldom prosecuted, and some graft investigations have come close to the president himself.
In Tokyo, representatives from some 70 countries and organizations planned to establish accountability guidelines to ensure that Afghanistan does more to improve governance and finance management, and to safeguard the democratic process, rule of law and human rights, especially those of women.
On the major non-NATO ally designation, Clinton said Afghanistan would have access to U.S. defense supplies and training and cooperation.
"This is the kind of relationship that we think will be especially beneficial as we plan for the transition," she said. "It will help the Afghan military expand its capacity and have a broader relationship with the United States."
Designating Afghanistan as a major non-NATO ally was part of a Strategic Partnership Agreement signed by Presidents Barack Obama and Karzai in Kabul at the beginning of May.
On Wednesday, the U.S. ambassador to Afghanistan, Ryan Crocker, and the country's foreign minister announced that the two countries had completed their internal processes to ratify the agreement, which has now gone into force.
Associated Press writer Patrick Quinn in Kabul contributed to this report.