KIEV, April 17 – Ukraine may use a recently opened probe against former Prime Minister Yulia Tymoshenko for legally challenging and canceling a 10-year natural gas agreement with Russia, First Deputy Prosecutor General Renat Kuzmin said Friday.

The warning comes days after Russian Prime Minister Vladimir Putin, during his visit to Kiev, has failed to agree to lower natural gas prices as Ukraine has persistently demanded over the past 12 months.