Jailed former Ukrainian prime minister Yulia Tymoshenko has called for a termination of the agreement that allows Russia to retain its naval base at Sevastopol until 2042.

This has been announced on Tymoshenko's Batkivshchyna party website on Friday.

The Russian Black Sea Fleet is stationed at the historic port of Sevastopol in Crimea under a lease agreement with Ukraine.

Moscow and Kiev resigned the so-called Kharkiv agreements on April 21, 2010, extending the fleet's lease to the base for another 25 years after the current lease expires in 2017.

However, this development was made possible only after Viktor Yanukovych, viewed as pro-Russian, won the Ukrainian presidential elections in February 2010, beating ex President and top political rival, pro-Western Viktor Yushchenko.

The Kharkiv agreements, which were ratified by parliament in April 2010, violate Ukrainian and international law, Tymoshenko said on Friday.

"The Ukrainian Constitution was violated. It clearly states: foreign military bases on Ukrainian territory shall not be permitted," Batkivshchyna quoted Tymoshenko as saying, reported RIA Novosti.

Tymoshenko, who is serving a seven-year prison term for abuse of office over the solution of the 2009 Russian-Ukrainian gas crisis on which she shook with Russian PM Vladimir Putin, has severe back pain and cannot walk. Tymoshenko herself says her sentencing is politically motivated by her rival, President Yanukovych.

Doctors from German clinic Charite who examined Tymoshenko diagnosed her with "an acute form of herniation of intervertebral disks" Dr. Karl Max Einhaeupl of Berlin's Charite clinic said.