Bratislava  - Calling Afghanistan "the most complex challenge NATO has ever undertaken," the alliance's secretary general called on Thursday for a greater commitment by member nations to bring stability and peace to the country and to prevent greater regional threats.

Rasmussen was speaking in the Slovak capital ahead of a meeting of member defence ministers that is not expected to yield any concrete decisions on Afghanistan or other alliance matters.

"I am well aware that there is an increasing number of people who are asking if the cost of our engagement in Afghanistan is too high," Rasmussen said. "To these people I want to say very clearly and unambiguously: The cost of inaction would be far higher."

He added: "The pressure on nuclear armed Pakistan would be tremendous. Instability would spread throughout Central Asia. And it would be only matter of time until we in Europe would feel the consequences of all of this."

Reiterating remarks he has made previously, the former Danish prime minister said that more effort should be made towards helping Afghans govern themselves and that this required more training and equipment for Afghan security forces.

Thursday marks the opening of a two-day ministerial meeting in Bratislava. Its focus is future NATO strategy in Afghanistan, NATO budget constraints, and a revamped missile shield to protect Europe from rogue states.

US Secretary of Defence Robert M Gates is expected to brief allies on Friday on the new missile defence system, to replace the recently scrapped Bush-era project.

Rasmussen's appeal for a new approach on Afghanistan comes amidst waning public support for the war and uncertainty regarding White House commitment to the surge strategy advocated by Stanley A. McChrystal, the commander of American and allied forces in Afghanistan. (dpa)