NATO releases images of tank presence near Russia 's border with Ukraine . Security service says a homemade bomb was left outside gate of president 's offices . Three Ukrainian soldiers died in attack by separatists . Ukraine 's President vows punishment for the shootdown .
NATO releases images showing tank presence near Russia 's border with Ukraine . Security service says a homemade bomb was left outside gate of President 's offices . Three Ukrainian soldiers killed in attack by separatists . Ukraine 's President vows punishment for plane shootdown .