Censor.NET reports citing Poroshenko's Twitter.
He wrote: "Over these almost two years, no proposals on Savchenko's exchange have been voiced by the credible sources in the Russian Federation."
Poroshenko also wrote on Facebook: "As the president of Ukraine, I am ready to use my constitutional right and exchange Nadiia Savchenko, do the utmost to return her home as soon as possible.
"I call on the world leaders to step up pressure on the Russian Federation for the sake of Nadiia's release. If it's about stiffening sanctions - it must be done!
"What is happening in Russia with the Ukrainian officer can not be considered a trial. This is a farce, a mockery of a trial. Nadiia Savchenko is a Ukrainian pilot. The officer did what any uniform-clad Ukrainian should do: protected her native land."
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