forward, i think we re fully prepared to do that. reporter: the kremlin demanding a guarantee ukraine won t join nato, as over 100,000 heavily armed russian troops mass on ukraine s borders. eyva. lavrovti d but blinken vowing a swift and severe response if they do, repeating president biden s warning after biden came under fire this week for saying quote, response. that went down badly with the soldiers here in eastern ukraine who ve been facing russian backed rebels for eight years. we re moving through the trenches towards front lines against russian-backed separatist forces. the failure to reach a political agreement has only made the tension here and the risk even greater. even our interview with lieutenant general alexander pavluk interrupted by gunfire. you it can t be an empire. don t know whether you heard that there. we just heard a gunshot