To "trigger" something is to do a small thing to make a bigger thing happen. If troops from one country fire upon troops from another country, that may "trigger" a war. To say a war is "outright" is to say that it's official now, the countries are at war. When two countries that aren't friendly with each other have fights along the border, that's armed conflict, and people may die, but it isn't war. Such skirmishes may "trigger" a war by really pissing off the leaders of one of the countries. If one of those leaders says, "That's it, those Klingons have gone too far." and declares war, "outright" war was "triggered" by the skirmish.
So you're basically right. "My try is: "Mr Yatsenyuk wants to make sure if the takeover of the peninsula was a part of a dirty plan to suddenly starting a clear war."
You've got some minor, picky stuff to clean up to make the sentence a bit clearer, and some of your grammar is incorrect, but I think you're pretty close to getting the meaning right. One thing that might be a bit off is "make sure". To make sure of something is to confirm what you already believe. I think you mean to show Mr Yatsenyuk as inquiring with an open mind, not confirming what he already thinks he knows.
To just make the original line simpler, you could replace the word "trigger" with "start" and delete the word "outright". "Start a war" as opposed to "trigger an outright war". That's fine, and the meaning of the original line would stay largely intact.