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In response to Russian Defense Ministry's statement earlier on Monday that a Ukrainian military plane flew within 3 to 5 km of the Malaysian plane at the time in was downed, Poroshenko told CNN: "My immediate reaction - this is not true."
He said Ukraine was open to any investigation about its planes and that the Russians should provide evidence for such a statement.
Poroshenko also said that at the time of the incident the air space over eastern Ukraine was being monitored by various surveillance systems.
"Everybody knows that in this period of time when the tragedy happened all Ukrainian planes were on the ground (in the area)," he told CNN in an interview.
According to a transcript of the interview posted on his website, Poroshenko also aired the idea of asking the United States to grant Ukraine a special status as a so-called Major Non-NATO Ally, the same status now enjoyed by Israel, Egypt and Australia.
Any beefing up of ties between Kiev and Washington is all but certain to upset Moscow, which sees the former Soviet bloc as its special sphere of influence.