"Putin’s visit to Ukrainian Crimea without any agreement with the Ukrainian government is a challenge for the entire civilized world," Poroshenko wrote on his Facebook page.
Nevertheless, the Ukrainian president did not bother to explain why the Russian president should have authorization from Ukraine to visit one of the regions in his country.
On Monday, Putin arrived to Crimea to take part in a Russian State Council meeting on tourism.
The Republic of Crimea reunited with Russia in March 2014, following a referendum when most of its resident said yes to joining Russia. Ukraine and many Western countries have not recognized the vote.