Kyiv and Moscow are accusing each other of fueling tensions, as fighting in eastern Ukraine continues to escalate.
Ukrainian President Petro Poroshenko denounced President Vladimir Putin's arrival Monday in Crimea.
In a Facebook posting, Poroshenko called the Russian leader's visit to the Black Sea peninsula "a challenge to the civilized world and the continuation of the scenario to fuel tensions, which is being implemented by the Russian military and their mercenaries" in eastern Ukraine.
Putin held a meeting of his advisory State Council in the Crimean resort city of Yalta to discuss the development of tourism in Russia.
At least seven people were killed in eastern Ukraine overnight in fighting between government forces and Russia-backed separatists.
Local officials reported two civilians were killed in shelling near the government-controlled southeastern port city of Mariupol, while rebel officials said at least three civilians were killed in shelling near the separatist stronghold of Donetsk.
Ukraine's military reported two of its soldiers were also killed.
Ukraine's Foreign Ministry issued a statement calling for Moscow to "stop the escalation of the situation" in Ukraine and implement the provisions of the cease-fire agreements signed in Minsk, Belarus, particular those regarding the cease-fire and withdrawal of heavy weapons.
Earlier Monday, Russian Foreign Minister Sergei Lavrov blamed the Ukrainian government for the escalation in fighting, saying the developments of the last few days "look very much like preparation for fresh hostilities."
In a newspaper interview on Sunday with Bild am Sonntag, German Foreign Minister Frank-Walter Steinmeier said the situation in eastern Ukraine was "explosive" and called on the warring sides to return to the peace process to prevent "a new military escalation spiral."