This was reported on the website of the State Border Service of Ukraine.
According to the ministry, during the verification of one of them it turned out that he "illegally visited the territory of Crimea occupied by his country."
"The border guards refused to cross the border, and also informed about the ban on entry into the territory of our state and put a mark in the passport document," the statement said.
It is also reported that three more Russians "could not explain the expediency and purpose of their stay in Ukraine."
Earlier, the border service of Ukraine reported that passenger traffic on the border with Russia decreased by almost 10% in 2019.
Crimea became the Russian region after a referendum held there in March 2014, in which most residents spoke out for reunification with Russia.