Tom Koenigs told the online version of newsweekly Der Spiegel that in particular Germany, which has about 3,000 troops in the country, should send more soldiers and instructors to train the Afghan army and police force.

"Most Afghans do not want fewer but more Western troops to improve security," he said, noting that the United States and Britain had beefed up their military presence in the country.

In light of a heated debate in Germany about the future and goals of its engagement in Afghanistan, Koenigs said even a partial withdrawal would be "the worst thing one could do."

"A reduced engagement would immediately be read by the Taliban as weakness and thus exploited for propaganda," said Koenigs, who is a member of the German Greens party.

He called for patience in the West while international peacekeepers and local authorities improve their cooperation.

"Anyone who wants to pull out now will be leaving the Afghan people in the lurch and abandon them to a terrible, brutal movement," Koenigs said.

The top US commander in Afghanistan General Dan McNeil reiterated a call for Nato countries to contribute more soldiers to the battle against Taliban insurgents, in an interview with Saturday's issue of the German daily Die Welt.

The German parliament is due to vote on extending its military deployment in Afghanistan in September or October.

A charged debate about the mission has already broken out in the wake of the recent kidnapping of two Germans by the Taliban.