NATO members began a two-day meeting Wednesday at the alliance's headquarters in Brussels to develop an Afghanistan plan that will be discussed in Chicago, including "how we will complete transition to lead Afghan security responsibility ... and how we will continue to support Afghanistan after 2014," Rasmussen said.
Rasmussen said his message to insurgents is clear.
"You can't just wait us out," he said. "As we gradually draw down, a still stronger Afghan security force is taking charge to protect the Afghan people against brutality and inhumanity."
He said NATO would support the Afghan security forces beyond 2014, the scheduled pullout of coalition troops, through training and financial backing.
"We must make sure we maintain the gains made with so much investment in lives and resources," Rasmussen said.
He said he wants to assure the Afghan citizens that the coalition forces were committed a long-term partnership with Afghanistan.
Also at the May 20-21 Chicago summit, NATO members will "celebrate the vital link between America and Europe" and invest in that trans-Atlantic link that "remains as critical to our security in the future, as it has been in the past," he said.
"We will ensure that our alliance has the modern, deployable and connected forces that we need for the next decade and beyond," Rasmussen said. "We will do this through a renewed culture of cooperation we call smart defense."
He also said he expected the Chicago summit would include discussions on an interim missile defense capability that could be a "first step towards our long-term goal of providing missile defense for NATO's European populations, territory and forces."