"The representative office of the President of Ukraine in the Autonomous Republic of Crimea notes the unlawfulness of launching a rail link between Russia and the territory of Ukraine temporarily occupied by Russia - the Autonomous Republic of Crimea and the city of Sevastopol," the statement said.
Kiev believes that the launch of trains on the bridge violates the norms and principles of international law.
They also condemned the "inconsistent with Ukraine" visit to Crimea of Russian leader Vladimir Putin.
December 23, Putin attended the opening ceremony of the Crimean bridge railway.
The head of Crimea Sergey Aksyonov called the launch of trains on the bridge a historic event.
“Kryminform” also broadcast on the issue of a special brand of 50-ruble denomination on the occasion of the launch of railway communication on the Crimean bridge.
Crimea became the Russian region after a referendum held there in March 2014, in which most residents spoke out for reunification with Russia.