THE Taliban have ''overwhelmed'' foreign troops and cannot be defeated by military means, one of Australia's top combat soldiers has warned.

Brigadier Mark Smethurst says securing Afghanistan could take decades, but success is uncertain without a fundamental change in strategy.

His critical assessment comes in a report that contrasts sharply with federal government claims of progress in Afghanistan.

While the key role of Australian troops is mentoring local forces, he says the Afghan army cannot operate independently, despite seven years of training, and the police are even worse.

The Afghan government is ineffective and has failed to deal with corruption, human rights abuses and a non-existent justice system. Aid distribution, he says, has been ''wasteful, ineffective and insufficient''.