Addressing the Ukrainian people in an open letter posted in Ukrainian on the website of her party Fatherland late Monday, Tymoshenko called her hunger strike "a sign of unity and solidarity" with several hundred activists who have been staying in tents in the streets of Kiev since Sunday.
"Don't backtrack! Don't let them break our life! Go forward and win!" Tymoshenko said.
"And if on Nov. 29 Yanukovych fails to sign the association agreement, wipe him together with his corrupt cancer off the face of Ukraine by peaceful and constitutional means," Tymoshenko said, apparently referring to the fall of his government.
Tymoshenko's appeal was read out in Russian to protesters in Kiev late Monday, Ukrainskaya Pravda reported.
Ukraine had planned to seal the European deal at a two-day Eastern European Partnership Summit in Vilnius, Lithuania, at the end of this week until the Ukrainian government suspended the deal last Thursday over unspecified national security concerns.
Lithuania later accused Russia of pressuring Ukraine to postpone the deal, and Ukrainian opposition leader Arseny Yatsenyuk speculated that Russia had bribed Ukraine to delay it.
The European Union says the imprisonment of pro-Western Tymoshenko, who was the main competitor of pro-Russian Yanukovych in the 2010 presidential election, is politically motivated, and for the last two years has named her release a condition for signing the association agreement with Ukraine.
Tymoshenko is serving a seven-year prison term after a Kiev court in October 2011 convicted her of abuse of authority in signing gas contracts with Russia as prime minister in 2009.
Since 2010, the European Parliament has passed a number of resolutions calling Tymoshenko's prosecution politically motivated.On Thursday, the Ukrainian parliament, the Verkhovnaya Rada, rejected six bills that would have authorized Tymoshenko to undergo treatment in Germany for back problems.