Story highlights Russia claims to have foiled a Ukraine militant attack near Crimea

Ukraine denies the accusation from Russia, calling it "insane"

(CNN) Ukraine is ordering its troops to be on the "highest level of combat readiness" Thursday, amid growing tensions with Russia over Crimea.

The order comes after Russia accused Ukraine on Wednesday of launching a militant attack at "critically important infrastructure" near the city of Armyansk, Crimea, according to Russia's state news service TASS.

But Ukrainian President Petro Poroshenko refuted the claims, calling them "insane" and suggesting Russia's aim was more military threats against its neighbor.

The spat has seen tensions between the countries rise to their highest level since Russia annexed Crimea in 2014.

Violent clashes on the streets of Ukraine between pro-European activists and pro-Russian supporters in early 2014 set the scene for the annexation.

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