There is also a danger of Afghan soldiers switching sides for reasons other than radicalization, such as the perception that the Taliban is winning.

The U.S. withdrawal plan is based on the assumption that the surge, which is often compared to the one in Iraq, will work, he said.

But whereas Iraq boasts much infrastructure and a high rate of literacy, Afghanistan is an impoverished country with a largely illiterate population and a highly complex tribal structure, he said.

The bulk of U.S. and NATO ground forces will likely leave by 2014 -- the deadline at which Karzai promised to ready his forces -- but the country could end up resembling a post-Soviet invasion period, which left a power vacuum that the Taliban later filled, he contended.

Corruption in the security forces is another major problem.

"High ranking government officials are all from one tribe or clan and once the security handover takes place, all the funds will be spent in one part of the country, while other parts may suffer," said Noori Zabihullah, an independent Afghan journalist based in Mazar-i- Sharif, Afghanistan.

And while Afghans regard their army as capable, the police are widely considered corrupt, with district level police chiefs appointed based on personal connections, he said.

"Traffic police chiefs are the same, simply because they can make lots of money by issuing vehicle registration documents and driving licenses," he said via email.

U.S. chairman of the joint chiefs of staff Admiral Mike Mullen, however, called the 2014 deadline "reasonable," adding that he remained optimistic that the U.S. surge will thwart the Taliban, drawing a comparison with the U.S. surge in Iraq.

The 2014 deadline does not mean Afghanistan will get rid of all of its military partners, said Anthony H. Cordesman, former director of intelligence assessment in the Office of the Secretary of Defense and now at the Center for Strategic and International Studies.

Iraq' s government, he noted, took over responsibility in many areas more than a year before U.S. forces began to seriously withdraw.

"This transition is one where you don't abandon the government and say 'sorry we' re leaving, regardless of whether you have the experience and capability to be ready.' "

Setting up facilities, partnering and training new units takes time. "You don't suddenly create an instant army," he said.