The Ukrainian foreign ministry Monday lodged a protest with Russia over a visit by Russian Prime Minister Dmitry Medvedev to Crimea.
"The visit of a foreign official to Ukraine without proper and prior agreement with the Ukrainian side is a gross violation of existing norms of interstate relations," Xinhua quoted foreign ministry spokesperson Eugene Perebiynis as saying.
Earlier in the day, Medvedev arrived in Crimea for talks with the region's leaders on economic and social development.
Medvedev's visit came two weeks after Russian President Vladimir Putin and Crimean leaders signed a treaty to make the peninsula part of Russia following a March 16 referendum, during which over 96 percent of Crimean voters chose to join Russia.
Kiev does not accept Crimea's accession to Russia, considering it an "attempt to annex the Ukrainian territory".