Rasmussen signed an agreement with Japanese Prime Minister Shinzo Abe that outlines stronger bilateral ties.
"While NATO has no ambition to take on a permanent role in Asia, we see very clearly the advantage of working with like-minded partners like Japan," Rasmussen said in a statement Monday.
The declaration is the first agreement between NATO and Japan. Japan, however, has worked alongside NATO forces in operations in Afghanistan.
"We are natural partners and together we can make a difference," Ramussen said.
Rasmussen's visit comes amid heightened tensions on the Korean Peninsula. North Korea tested a nuclear device in February and has since escalated its war rhetoric.
The U.S. Defense Department is changing its focus to the Asia-Pacific as military engagement with Iraq has ended and the Afghan war draws to a close. The U.S. military has said about 60 percent of its naval assets would be assigned to the region by 2020.