"If Putin wants to defeat Ukraine, he'll have to try to defeat me first! But if he wants peace and friendship between our nations as he claims," she added, "I am ready to make the first step towards it. My freedom will be that first step towards peace and understanding in Ukraine," she wrote.
Russia claims the 33-year-old is behind the killings of two Russian journalists hit by mortar fire at a checkpoint in eastern Ukraine, allegations she has always denied. Moscow says she then crossed voluntarily into Russia and sought asylum as a refugee. The Ukrainian government, however, insists she was kidnapped by rebel forces and that she is a prisoner of war.
"I have already been in captivity for an hour when those Russian journalists died. I have not seen them, and our ways have never crossed. The 'rebels' themselves told me that those journalists came under fire of their own 'makhnovtsi' [slang for 'anarchists']," Savchenko told CNN in her letter from jail.
"And the investigators knew all about it since the very beginning! And they have nothing on me! They simply thought that it would be easy to "twist my arms" and receive another star for their epaulettes. But it's not going to happen!" she added.
Despite her critical situation, Savchenko appears to have retained her sense of humor just as much as her determination, writing that she was feeling "On the edge!...;) Close to Nirvana and enlightenment!;) Joking."
"Holding on! But holding my body entirely on the power of my will because I am so numb that I couldn't feel the needle when the blood sample was taken from my vein today. Tottering, head is spinning, [blood] pressure 80x40, [blood] sugar 2.9, T [temperature] - 35.7°C. But still be standing till 50 kg [body weight]! Even longer if God let's me! Hasn't fainted even once and hasn't fallen off my feet," Nadiya wrote.
The military pilot told CNN she is being monitored "24 hours a day," which she finds "very annoying."
"Protection and security measures are such that King Kong would not have been able to break away!;)," she joked again.
"But in general all is very decent and polite! Treatment is reasonable."