Six years and $16.5 billion later, the U.S. still lacks a solid plan to create a self-sustaining security force in Afghanistan, a new independent audit finds.

The Government Accountability Office found in a report released Wednesday that "some progress" has been made in training and equipping Afghanistan's army and police forces, but the Defense and State departments "lacked detailed plans and cost estimates for completing and sustaining" the forces.

The audit comes as violence in Afghanistan is on the rise and the U.S. is pleading with NATO allies to send more troops and trainers. Last month, American and allied combat deaths in Afghanistan passed the monthly toll in Iraq for the first time.

GAO said the U.S. government must more clearly define its objectives, set milestones and lay out a concrete spending plan for future requirements.

"We concluded that, without capable and self-sustaining Afghan army and police forces, terrorists could again create a safe haven in Afghanistan and jeopardize efforts by the United States and the international community to develop the country," GAO wrote.

The Pentagon defended progress made in the effort and said it planned to release its own assessment soon.

"We believe it's well reasoned, that it is a successful program that is building on the Afghan government's capacity to respond to the insurgency, provide stability and implement the rule of law throughout Afghanistan," said Defense Department spokesman Bryan Whitman.

But lawmakers said they remained concerned that the war effort there was being shortchanged because of the U.S. focus on Iraq.

"I'm just struck with the fact that we are so far behind in Afghanistan that it's more than alarming," said Rep. Christopher Shays, R-Conn. "I don't see anything that makes me feel encouraged. And I think the thing that concerns me the most is that some of this appears to be extraordinarily bad planning."

As an example of slow progress, GAO found that only two out of 105 Afghan army units were deemed "fully capable" while 65 were still in training or deemed mostly unable to conduct their missions. The remaining units were considered capable but only with international assistance.

No Afghan police unit is considered fully capable, GAO says.

The U.S. has spent more than $10 billion to develop the Afghan army and $6 billion on its police forces since 2002.