Yulia Tymoshenko, Ukraine’s jailed ex-prime minister, has called on the country’s opposition forces to unite in the face of “the enemy from within”.

Several thousand opposition members gathered on Sunday on Sofiyska and Mikhaylovskaya squares, downtown Kiev, to mark the Ukrainian Unification Day, when the declaration of 1919 was signed uniting the Ukrainian lands.

Tymoshenko managed to pass a letter to participants of the rally and her message was read out by the deputy head of her Batkivshchyna party, Alexander Turchinov. “The enemy from within is more dangerous than an outside enemy,” Tymoshenko said in the letter.

According to Tymoshenko, “Mafia came to power in Ukraine,” and it is not only destroys and kills the Ukrainian values from within, but also puts in jeopardy the independence of Ukraine. Tymoshenko also urged opposition parties to unite. Former prime minister promised her followers that she would hold on and continue fighting.

In October, Tymoshenko was found guilty of abuse of office when she signed gas deals with Russia in 2009. She has been sentenced to seven years in jail and ordered to pay $187 million in damages to the Naftogaz company. Tymoshenko said the charges against her were President Viktor Yanukovych's political revenge, which he has denied.

Tymoshenko’s supporters believe the prosecution is politically motivated. The Ukrainian authorities deny the accusations.