The Cooperative Key 2001 started with a moment of silence in memory of the victims from the terrorist acts in the US. `We condemn the terrorist acts in the US, which are an attack on humanity and everything we believe in,` General Francisco de la Vega, co-director of the exercise, said at the opening ceremony, quoted by BTA. General Miho Mihov, Chief of the Bulgarian General Staff also expressed his concern and sympathy on the tragic incident. General Mihov Staff also said that the exercise was a major moment in Bulgaria`s preparation for NATO membership with both military and political significance. Wishing the participants success, General Mihov announced the start of the Cooperative Key exercise. `All the necessary measures have been taken to ensure the security of the US participants in the exercise, `the Bulgarian co-director, Major General Dimitur Tsvetkov said after the ceremony. General Mihov said that for the time being the alert status of the Bulgarian army is not being considered. The Partnership for Peace air force exercise is conducted by the Allied Forces Southern Europe with the participation of the Partner countries.