Germany's offer to station 600-800 troops in Afghanistan after NATO's combat role ends next year could encourage others to step up to the plate, the head of the military alliance said Friday.

"I warmly welcome the German commitment ... to contribute in such a significant way," NATO chief Anders Fogh Rasmussen said.

Germany could "serve as an example ... an encouragement" to other countries who have forces under NATO command fighting the Taliban, Rasmussen told a press conference.

Berlin announced Thursday it could keep 600-800 troops in Afghanistan for two years from 2015 to help train and advise the national army in its battle against the Taliban.

The offer requires however that Kabul formally request the troop presence because "we want to be welcome," as well as a UN Security Council resolution, German Defence Minister Thomas de Maiziere said.

It would also require a reasonable security situation and matching commitments by NATO allies in other parts of the country, de Maiziere said.

Germany has the third-biggest foreign troop deployment in Afghanistan after the United States and Britain but has drawn down numbers from more than 5,000 to 4,200 now.

The alliance plans to keep 8,000 to 12,000 troops in the country from 2015 to train and assist the Afghan army as it takes on full responsibility for national security.

There are currently some 100,000 troops under NATO command in Afghanistan, including 68,000 US soldiers whose numbers will be cut by roughly half this year.