KIEV, June 23 - Former presidents Leonid Kravchuk, Leonid Kuchma and Viktor Yushchenko have written an open letter to Russian President Vladimir Putin urging him to to stop his aggression against Ukraine.

"We have signed an open letter to Russian President Vladimir Putin that it is necessary to stop aggression. Ukraine is ready for negotiations," first Ukrainian President Kravchuk told reporters on June 22 after laying flowers at the Tomb of Unknown Soldier in Kiev on the day of mourning and memory of war victims.