Ukrainian Defence Council spokesman Andriy Lysenko says the military will be ready to respond: "If there is direct aggression, then it is obvious that there will be an adequate answer from all branches of Ukrainian armed forces."
The battle between Ukraine government troops and separatist rebels has been raging since April.
Economic sanctions from the West, and threats of further action against Russia, have had little affect.
And Wednesday Russian president Vladimir Putin ordered sanctions of his own.
The misery continues in Donetsk, with some accusing their government of heavy-handedness, using warplanes to bomb the rebels into submission.
"Genocide, in my opinion it's genocide. To kill people for nothing," says Donetsk resident Olga.
As workers try to put the broken pieces back together, Ukraine's military prepares for a bigger battle they believe is still to come.