Australian Foreign Minister Alexander Downer has said Australian troops will need to stay in Afghanistan for years to buttress international efforts to defeat the Taliban and establish a secure state.

Downer made an unannounced visit to Afghanistan during the weekend and met with Afghanistan's President Hamid Karzai.

After their meeting, Downer warned that Afghanistan "is a struggle for the long haul."

"I believe Australian troops will be in Afghanistan for years," he told The Australian, one of the leading newspapers in Australia.

This view is driven by the backwardness of the country, the scale of the threat, and the risk to Australia and other nations of allowing the Taliban to regain influence and export jihadist terror, said the newspaper Monday.

After two days visiting Australian forces in southern Uruzgan province and in Kabul, Downer left distinctly more optimistic, unconvinced by gloomy assessments provided by Australian intelligence, according to the newspaper.

"There has been a lot of military activity in Afghanistan in recent times and much of it has been successful," he said of the combined efforts of the North Atlantic Treaty Organization International Security Assistance Force (ISAF) and the U.S. Operation Enduring Freedom.

"I come away more optimistic," he said.