NATO's outgoing Secretary-General Jaap de Hoop Scheffer says the alliance's mission in Afghanistan is essential to international security and that leaving the country would leave the way open for a return of al Qaida.  Speaking in London on Monday, two weeks before he finishes his tenure, Scheffer said the alliance has made progress, but faces challenges in the 21st century and must adapt to the modern world.  

Jaap de Hoop Scheffer says NATO cannot abandon Afghanistan, even though it presents challenges to the NATO countries fighting there.

"If we would run and if we would lose, the consequences would be dire, not only for Afghanistan, Pakistan and the region, but certainly also for us here in the United Kingdom or in the Netherlands or Belgium for that matter," said Jaap de Hoop Scheffer.

De Hoop Scheffer says if Afghanistan fell to the Taliban, extremism would spread and al-Qaida would have a free hand to expand its global terrorist ambitions.

The outgoing NATO secretary general says in the 21st century the use of force is necessary in Afghanistan and elsewhere because of the changing nature of security risks.

"We must accept that security today requires engagement in far away places - engagement that is dangerous," he said. "It is expensive, and I say it not always has the guarantee of success."

Critics say NATO's performance in Afghanistan has shown cracks in the alliance - not enough political will among members, poor logistical coordination and no cohesive command structure.

In moving forward, de Hoop Scheffer says NATO must develop more flexible fighting forces, broaden its political dialogue, and develop global partnerships, including creating structures in which non-member countries can participate.

"NATO can no longer be a solo-player," said Jaap de Hoop Scheffer. "Quite the contrary.  True success in Afghanistan requires civil reconstruction - something which NATO cannot provide, but which others must supply.  If these other actors do not engage, NATO cannot truly succeed either."

De Hoop Scheffer calls NATO a timeless alliance, but one that must adapt.

De Hoop Scheffer was speaking at London's Chatham House research center.  He hands over the helm of NATO to former Danish Prime Minister Anders Fogh Rasmussen on July 31.