MOSCOW, November 25. /TASS/. The passage of civil ships through the Kerch Strait was banned on Sunday amid fears of provocations after three Ukrainian warships had intruded into Russia’s territorial waters, a source in transport authorities of the South Federal District told TASS.

"The Kerch-Yenikale Canal has been closed," the source said, noting that this comes "amid fears of provocations" and earlier political statements in Ukrainian media.

Besides, the ships have switched off all means of their detection, he said. "They are not seen, they are not providing information to the center for control of maritime traffic."

Earlier on Sunday, the Russian Federal Security Service’s Border Service in Crimea reported that three Ukrainian warships had illegally crossed Russia’s state border entering its territorial waters, and were carrying out dangerous maneuvers.

A source in law enforcement agencies of the South Federal District identified these vessels as two small armored boats Berdyansk, Nikopol and tugboat Krasnoperekopsk (which was renamed by Ukraine).

The Ukrainian warships continue heading to the Kerch Strait.

The Treaty on the Legal Status of the Sea of Azov and the Kerch Strait, signed in 2003, confirmed their status as domestic waters of Russia and Ukraine. The sides agreed on the joint usage and protection of the Sea of Azov and the Kerch Strait and introducing restrictions for vessels of third countries.