"The world must provide assessment of sharp aggravation of the situation in Ukraine," he said in a statement on his website.
So far, the U.S. response to reports that Russian troops had helped separatists capture the strategic southeastern town of Novoazovsk has been restrained, with State Department spokeswoman Jen Psaki saying Wednesday that the matter "is of deep concern to us."
White House spokesman Josh Earnest was more specific, noting in response to reporters' questions Wednesday that the reports had not been confirmed, but if true "these are the same kinds of activities that the international community has called on [Russian] President [Vladimir] Putin to end, and these are the same kinds of military activities that have earned or caused the international community to impose a pretty significant cost on the Russians and on the Russian economy as a result.
"What we would like to see is Russia to roll back their military from across the border, to stop providing weapons and materiel and training to the separatists, and to use their influence with the separatists to try to reach a political agreement with the Ukrainian government," Earnest said.
Though the Obama administration's attention in recent days has been focused on the threat from the Islamic State of Iraq and Syria, Poroshenko's request may bring Ukraine back to the forefront.