Nuclear bombs are stored on air force bases in Italy, Belgium, Germany and the Netherlands. The Federation of American Scientists [2](FAS) estimates that there are some 200 B61 thermonuclear gravity bombs scattered across these four countries. Under a NATO agreement struck during the Cold War, the bombs, which are technically owned by the U.S., can be transferred to the control of a host nation's air force in times of conflict.
Links
[1] https://www.ploughshares.org/file/1346
[2] http://www.fas.org
[3] http://www.ploughshares.org/expert/136
[4] http://www.time.com/time/world/article/0,8599,1943799,00.html