KIEV, April 26 – Ukraine has tightened security measures at its nuclear power plants because of fear of Russian aggression and the failure of the security guarantees granted under the Budapest Memorandum in exchange for giving up its nuclear arsenal, President Petro Poroshenko said.

"The Kremlin's refusal to recognize Ukraine's independence and the lack of effective security guarantees for a nuclear-weapon-free Ukraine in the Budapest Memorandum, in turn, triggered Russia's attack on our independent state. The Russian aggression firstly undermined the confidence of non-nuclear states in the regime of non-proliferation of these weapons and secondly created a threat of recurrence of the nuclear disaster on the territory of our state," Poroshenko said during a visit to Chernobyl on Tuesday.