The Security Service of Ukraine (SSU) has faced the challange to sophisticate actual and fundamentally new approaches, methods and means of countering threats to national security under conditions of the ongoing full-scale invasion of Russian troops and occupation the territory of Ukraine. The imposition of martial law in Ukraine has considerably expanded the range of practical tasks performed by the bodies and departments of the Security Service of Ukraine. The conditions of the intelligence activities, specific features of counterintelligence activities during the war have been forming new approaches of counterintelligence operations. These factors set and manage new operational and combat tasks for the Security Service of Ukraine. Moreover, SSU is an authorized body in the sphere of counterintelligence activities, that performs tasks of preventing, detecting and analyzing threats to the national security of Ukraine and make challenges to the vital interests of the state. The accomplishment of thesre tasks is plausible on the basis of efficient and prompt identification and threats prevention to the national security of Ukraine, identifying the sources of threats, origin and consequences in order to successfully select methods and means to counter them. The application peculiarities of the operational and combat methods and means by the counterintelligence units of the Security Service of Ukraine during the execution of operational and combat missions in the conditions of the ongoing Russian military aggression against Ukraine are considered in the study. It has been determined that under martial law the counterintelligence units have developed a set of measures to counteract the Russian special services activities as a result of the special tasks that are under provisions of the Security Service of Ukraine. This was accomplished due to the efficiency and enemy goals identification, thoroughly selected methods and forms to prevent intelligence and subversive activities, using appropriate means to overcome the enemy. Mainly, the Security Service of Ukraine adjusts to modern realities, changes, supplements and improves its methods of activity. The Security Service of Ukraine develops a far-sighted strategy, amends its skills with new tactical techniques, creates and uses cutting-edge operational and combat tools and methods, which are transformed and sophisticated in the conditions of war. All these measures prevent threats to national security posed by the enemy. These methods are successfully applied by the counterintelligence units of the Security Service of Ukraine during the execution of operational and combat tasks, and require further theoretical justification.