Ukraine's President Petro Poroshenko has responded to a letter from Ukrainian political prisoner Vololymyr Balukh, who is in Razdolnensky temporary detention facility in temporarily occupied Crimea.

"No one will overcome the people who sing the Ukrainian hymn in the Kremlin dungeons - despite bans and under the threat of severe punishment ... Thank you, Volodymr Balukh, for your letter and even more for your courage," Poroshenko said on his Facebook page on Sunday evening.

The head of state promised to continue work on the release of all Ukrainian political prisoners in Russia-occupied Crimea and Russia.

"We will continue our struggle for the liberation of all Ukrainian hostages in the Russia-occupied Donbas and Crimea, and we will not stop this struggle. I will do everything I can to hasten the moment when I can shake your hand on free Ukrainian soil," Poroshenko said.

As earlier reported, Ukrainian political prisoner Balukh wrote a letter to Poroshenko, in which he described how the anthem of Ukraine was sung in the Simferopol pretrial prison.