President Hamid Karzai said in a speech Tuesday negotiations on a mutual security agreement had stalled over the proposed guarantee, which he said should be put in writing as part of the pact.
Voice of America said the Obama administration has expressed a willingness to kick in as much as $4 billion per year but prefers to sign an agreement that is more-broadly based and doesn't include hard guaranteed figures.
The weekend attack on Kabul by Taliban commandos underscored the need for a crack military and police service in Afghanistan to maintain the peace once the United States and its allies pull out, VOA said.
Negotiations continue with the United States hoping to have an agreement signed before the NATO summit in Chicago next month.
Notable deaths of 2014 [PHOTOS]
Pakistan PM urges eradication of polio