"The border guard service of the Russian Federal Security Service takes all necessary measures to stop this provocation".
The agency, known as the FSB, said in a statement Sunday night that "there is irrefutable evidence that Kiev prepared and orchestrated provocations.in the Black Sea. These materials will soon be made public".
The Kerch Strait is the only passage into the Sea of Azov beyond it.
It later said Russian helicopters had also flown on an attack course at the vessels before veering off.
Today's incident began to unfold early on Sunday.
Russia has stopped three Ukrainian navy vessels from entering the Sea of Azov via the Kerch Strait by placing a huge cargo ship beneath a Russian-controlled bridge, Russia's state-controlled Rossiya 24 TV channel reported on Sunday.
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According to the Ukrainian Navy, vessels belonging to Russia's border service opened fire on the Ukrainian fleet, injuring six sailors, before seizing two of the ships.
Its tug, named Yana Kapu, allegedly suffered damage to its engine, guard rail and outer shell.
Ukraine said it gave Russian Federation advance warning of its ships' route, however.
The Kerch bridge is seen blocked for ships entrance, near Kerch, Crimea, Sunday, Nov. 25, 2018.
At the time of writing, dozens of cargo ships are stuck, awaiting for the passage to be reopened, based on AIS (Automatic Identification System), an automatic tracking system used by ships and Vessel Traffic Services (VTS) for identification and geo-localization of vessels, by mutually exchanging data with other ships and AIS Base stations.
Mariupol is close to the region of eastern Ukraine controlled by Russian-backed separatists in a conflict that has caused at least 10,000 deaths since 2014.
The global community has largely not recognized Russia's annexation of the Black Sea peninsula of Crimea from Ukraine.
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"It is clear that their goal is to create a conflict situation in the region".
The statement did not mention ramming the Ukrainian tugboat.
"We consider such aggressive actions as a violation of the norms of the UN Charter and the United Nations Convention on the Law of the Sea", the statement went on.
"Such actions pose a threat to the security of all states in the Black Sea region, " the statement said, "and therefore require a clear response from the global community".
A source in the Ukrainian Defense Ministry told the news portal InfoResist that six Ukrainian navy men had been wounded, two of them are in serious condition.
"What is happening now at the (Kerch) bridge threatens to become a very unpleasant story", said Kiselyov, one of the Kremlin's main propagandists.
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